diff --git a/src/blenderbim/blenderbim/bim/module/classification/operator.py b/src/blenderbim/blenderbim/bim/module/classification/operator.py
index 08020cef76..fa35886176 100644
--- a/src/blenderbim/blenderbim/bim/module/classification/operator.py
+++ b/src/blenderbim/blenderbim/bim/module/classification/operator.py
@@ -88,7 +88,7 @@ class AddManualClassificationReference(bpy.types.Operator, tool.Ifc.Operator):
         reference = ifcopenshell.api.run(
             "classification.add_reference",
             tool.Ifc.get(),
-            product=product,
+            products=[product],
             classification=classification,
             identification="X",
             name="Unnamed",
@@ -358,15 +358,18 @@ class AddClassificationReference(bpy.types.Operator, tool.Ifc.Operator):
                 classification = element
                 break
 
-        for obj in objects:
-            ifc_definition_id = tool.Blender.get_obj_ifc_definition_id(obj, self.obj_type, context)
-            if not ifc_definition_id:
-                continue
+        ifc_file = tool.Ifc.get()
+        products = [
+            ifc_file.by_id(ifc_definition_id)
+            for obj in objects
+            if (ifc_definition_id := tool.Blender.get_obj_ifc_definition_id(obj, self.obj_type, context))
+        ]
+        if products:
             ifcopenshell.api.run(
                 "classification.add_reference",
                 tool.Ifc.get(),
                 reference=IfcStore.classification_file.by_id(self.reference),
-                product=tool.Ifc.get().by_id(ifc_definition_id),
+                products=products,
                 classification=classification,
             )
 
@@ -414,7 +417,7 @@ class AddClassificationReferenceFromBSDD(bpy.types.Operator, tool.Ifc.Operator):
             reference = ifcopenshell.api.run(
                 "classification.add_reference",
                 tool.Ifc.get(),
-                product=element,
+                products=[element],
                 classification=classification,
                 identification=bsdd_classification.reference_code,
                 name=bsdd_classification.name,
diff --git a/src/ifcopenshell-python/ifcopenshell/api/__init__.py b/src/ifcopenshell-python/ifcopenshell/api/__init__.py
index 8f7b82351c..7c739cf71b 100644
--- a/src/ifcopenshell-python/ifcopenshell/api/__init__.py
+++ b/src/ifcopenshell-python/ifcopenshell/api/__init__.py
@@ -87,6 +87,9 @@ ARGUMENTS_DEPRECATION = {
     "material.unassign_material": partial(
         batching_argument_deprecation, prev_argument="product", new_argument="products"
     ),
+    "classification.add_reference": partial(
+        batching_argument_deprecation, prev_argument="product", new_argument="products"
+    ),
 }
 
 
diff --git a/src/ifcopenshell-python/ifcopenshell/api/classification/add_reference.py b/src/ifcopenshell-python/ifcopenshell/api/classification/add_reference.py
index 320825e335..9057f7a25f 100644
--- a/src/ifcopenshell-python/ifcopenshell/api/classification/add_reference.py
+++ b/src/ifcopenshell-python/ifcopenshell/api/classification/add_reference.py
@@ -17,12 +17,24 @@
 # along with IfcOpenShell.  If not, see <http://www.gnu.org/licenses/>.
 
 import ifcopenshell
+import ifcopenshell.api
+import ifcopenshell.util.element
 import ifcopenshell.util.schema
+from typing import Optional, Union
 
 
 class Usecase:
-    def __init__(self, file, product=None, reference=None, identification=None, name=None, classification=None, is_lightweight=True):
-        """Adds a new classification reference and assigns it to a product
+    def __init__(
+        self,
+        file: ifcopenshell.file,
+        products: list[ifcopenshell.entity_instance],
+        reference: Optional[ifcopenshell.entity_instance] = None,
+        identification: Optional[str] = None,
+        name: Optional[str] = None,
+        classification: Optional[ifcopenshell.entity_instance] = None,
+        is_lightweight=True,
+    ):
+        """Adds a new classification reference and assigns it to the list of products
 
         A classification reference is a single entry such as "Pr_12_23_34" that
         is part of an external classification system (such as Uniclass or
@@ -33,7 +45,7 @@ class Usecase:
         resources such as profiles, documents, libraries, and so on.
 
         Classification references can be added in two ways. Option 1) specify  a
-        custom arbitrary reference, where you have the manually specify the
+        custom arbitrary reference, where you have to manually specify the
         identification (e.g. "Pr_12_23_45") and name (e.g. "Door Products").
         Option 2) add a reference from an IFC classification library. The latter
         is preferred if you are using a common classification system such as
@@ -52,13 +64,13 @@ class Usecase:
         assigned to both the type and an occurrence, then the assignment at the
         occurrence will override the type classification.
 
-        :param product: The IFC object, property, or resource you want to
+        :param product: The list of IFC objects, properties, or resources you want to
             associate the classification reference to.
-        :type product: ifcopenshell.entity_instance.entity_instance
+        :type product: list[ifcopenshell.entity_instance.entity_instance]
         :param reference: The classification reference entity taken from an
             IFC classification library. If you supply this parameter, you will
             use option 2.
-        :type product: ifcopenshell.entity_instance.entity_instance, optional
+        :type reference: ifcopenshell.entity_instance.entity_instance, optional
         :param identification: If you choose option 1 and do not specify a
             reference, you may manually specify an identification code. The code
             is typically a short identifier and may have punctuation to separate
@@ -70,7 +82,7 @@ class Usecase:
         :param classification: The IfcClassification entity in your IFC model
             (not the library, if you are doing option 2) that the reference is
             part of.
-        :type product: ifcopenshell.entity_instance.entity_instance
+        :type classification: ifcopenshell.entity_instance.entity_instance
         :param is_lightweight: If you are doing option 2, choose whether or not
             to only add that particular reference (lighweight) or also add all
             of its parent references in the classification hierarchy (not
@@ -81,8 +93,12 @@ class Usecase:
             is generally unnecessary. Using lightweight classifications are
             recommended and is the default.
         :type is_lightweight: bool, optional
+
+        :raises TypeError: If file is IFC2X3 and `products` has non-IfcRoot elements.
+
         :return: The newly added IfcClassificationReference
-        :rtype: ifcopenshell.entity_instance.entity_instance
+            or `None` if `products` was empty list.
+        :rtype: Union[ifcopenshell.entity_instance.entity_instance, None]
 
         Example:
 
@@ -93,7 +109,7 @@ class Usecase:
             classification = ifcopenshell.api.run("classification.add_classification",
                 model, classification="MyCustomClassification")
             ifcopenshell.api.run("classification.add_reference", model,
-                product=wall_type, classification=classification,
+                products=[wall_type], classification=classification,
                 identification="W_01", name="Interior Walls")
 
             # Option 2: adding a popular classification from a library
@@ -104,12 +120,12 @@ class Usecase:
             reference = [r for r in library.by_type("IfcClassificationReference")
                 if r.Identification == "XYZ"][0]
             ifcopenshell.api.run("classification.add_reference", model,
-                product=wall_type, classification=classification,
+                products=[wall_type], classification=classification,
                 reference=reference)
         """
         self.file = file
         self.settings = {
-            "product": product,
+            "products": products,
             "reference": reference,
             "identification": identification,
             "name": name,
@@ -117,8 +133,27 @@ class Usecase:
             "is_lightweight": is_lightweight,
         }
 
-    def execute(self):
-        self.is_rooted = self.settings["product"].is_a("IfcRoot")
+    def execute(self) -> Union[ifcopenshell.entity_instance, None]:
+        if not self.settings["products"]:
+            return
+
+        if self.settings["reference"]:
+            referenced = ifcopenshell.util.element.get_referenced_elements(self.settings["reference"])
+            if set(self.settings["products"]).issubset(referenced):
+                # nothing to do, all elements already have this reference assigned
+                return self.settings["reference"]
+
+        self.rooted_products: set[ifcopenshell.entity_instance] = set()
+        self.non_rooted_products: set[ifcopenshell.entity_instance] = set()
+        for product in self.settings["products"]:
+            if product.is_a("IfcRoot"):
+                self.rooted_products.add(product)
+            else:
+                self.non_rooted_products.add(product)
+
+        if self.non_rooted_products and self.file.schema == "IFC2X3":
+            raise TypeError(f"Cannot add reference to non-IfcRoot element in IFC2X3: {self.non_rooted_products}.")
+
         if self.settings["reference"]:
             return self.add_from_library()
         return self.add_from_identification()
@@ -134,14 +169,10 @@ class Usecase:
             else:
                 reference.Identification = self.settings["identification"]
 
-        relationship = self.get_existing_relationship(reference)
-        if relationship:
-            self.add_to_existing_relationship(relationship)
-        else:
-            self.add_new_relationship(reference)
+        self.update_relationships(reference)
         return reference
 
-    def add_from_library(self):
+    def add_from_library(self) -> ifcopenshell.entity_instance:
         if hasattr(self.settings["reference"], "ItemReference"):
             identification = self.settings["reference"].ItemReference  # IFC2X3
         else:
@@ -155,8 +186,9 @@ class Usecase:
                 old_referenced_source = self.settings["reference"].ReferencedSource
                 self.settings["reference"].ReferencedSource = None
             else:
+                classification_name = self.settings["classification"].Name
                 existing_classification = [
-                    c for c in self.file.by_type("IfcClassification") if c.Name == self.settings["classification"].Name
+                    c for c in self.file.by_type("IfcClassification") if c.Name == classification_name
                 ]
 
             reference = migrator.migrate(self.settings["reference"], self.file)
@@ -174,15 +206,10 @@ class Usecase:
                 for element in to_delete:
                     self.file.remove(element)
 
-        relationship = self.get_existing_relationship(reference)
-        if relationship:
-            self.add_to_existing_relationship(relationship)
-        else:
-            self.add_new_relationship(reference)
-
+        self.update_relationships(reference)
         return reference
 
-    def get_existing_reference(self, identification):
+    def get_existing_reference(self, identification: Optional[str] = None) -> Union[ifcopenshell.entity_instance, None]:
         for reference in self.file.by_type("IfcClassificationReference"):
             if self.file.schema == "IFC2X3":
                 if reference.ItemReference == identification:
@@ -191,39 +218,39 @@ class Usecase:
                 if reference.Identification == identification:
                     return reference
 
-    def add_new_relationship(self, reference):
-        if self.is_rooted:
-            self.file.create_entity(
-                "IfcRelAssociatesClassification",
-                GlobalId=ifcopenshell.guid.new(),
-                RelatedObjects=[self.settings["product"]],
-                RelatingClassification=reference,
-            )
-        else:
-            self.file.create_entity(
-                "IfcExternalReferenceRelationship",
-                RelatingReference=reference,
-                RelatedResourceObjects=[self.settings["product"]],
-            )
-
-    def add_to_existing_relationship(self, rel):
-        if self.is_rooted:
-            related_objects = set(rel.RelatedObjects)
-            related_objects.add(self.settings["product"])
-            rel.RelatedObjects = list(related_objects)
-        else:
-            related_objects = set(rel.RelatedResourceObjects)
-            related_objects.add(self.settings["product"])
-            rel.RelatedResourceObjects = list(related_objects)
-
-    def get_existing_relationship(self, reference):
-        if self.is_rooted:
+    def update_relationships(self, reference: ifcopenshell.entity_instance) -> None:
+        root_rel, non_root_rel = None, None
+        if self.rooted_products:
             if self.file.schema == "IFC2X3":
                 for rel in self.file.by_type("IfcRelAssociatesClassification"):
                     if rel.RelatingClassification == reference:
-                        return rel
-            elif reference.ClassificationRefForObjects:
-                return reference.ClassificationRefForObjects[0]
-        elif self.file.schema != "IFC2X3":
-            if reference.ExternalReferenceForResources:
-                return reference.ExternalReferenceForResources[0]
+                        root_rel = rel
+                        break
+            else:
+                root_rel = next(iter(reference.ClassificationRefForObjects), None)
+
+            if root_rel:
+                related_objects = set(root_rel.RelatedObjects) | self.rooted_products
+                root_rel.RelatedObjects = list(related_objects)
+                ifcopenshell.api.run("owner.update_owner_history", self.file, **{"element": root_rel})
+            else:
+                self.file.create_entity(
+                    "IfcRelAssociatesClassification",
+                    OwnerHistory=ifcopenshell.api.run("owner.create_owner_history", self.file),
+                    GlobalId=ifcopenshell.guid.new(),
+                    RelatedObjects=list(self.rooted_products),
+                    RelatingClassification=reference,
+                )
+
+        if self.non_rooted_products:
+            # NOTE: Only Ifc4+. Ifc2x3 is already handled by raising TypeError
+            non_root_rel = next(iter(reference.ExternalReferenceForResources), None)
+            if non_root_rel:
+                related_objects = set(non_root_rel.RelatedResourceObjects) | self.non_rooted_products
+                non_root_rel.RelatedResourceObjects = list(related_objects)
+            else:
+                self.file.create_entity(
+                    "IfcExternalReferenceRelationship",
+                    RelatingReference=reference,
+                    RelatedResourceObjects=list(self.non_rooted_products),
+                )
diff --git a/src/ifcopenshell-python/ifcopenshell/api/classification/remove_reference.py b/src/ifcopenshell-python/ifcopenshell/api/classification/remove_reference.py
index 48b55b3740..b91989a1ae 100644
--- a/src/ifcopenshell-python/ifcopenshell/api/classification/remove_reference.py
+++ b/src/ifcopenshell-python/ifcopenshell/api/classification/remove_reference.py
@@ -44,7 +44,7 @@ class Usecase:
             classification = ifcopenshell.api.run("classification.add_classification",
                 model, classification="MyCustomClassification")
             reference = ifcopenshell.api.run("classification.add_reference", model,
-                product=wall_type, classification=classification,
+                products=[wall_type], classification=classification,
                 identification="W_01", name="Interior Walls")
             ifcopenshell.api.run("classification.remove_reference", model,
                 reference=reference, product=wall_type)
diff --git a/src/ifcopenshell-python/test/api/classification/test_add_reference.py b/src/ifcopenshell-python/test/api/classification/test_add_reference.py
index 7cf5722b8f..ed52b05d35 100644
--- a/src/ifcopenshell-python/test/api/classification/test_add_reference.py
+++ b/src/ifcopenshell-python/test/api/classification/test_add_reference.py
@@ -16,6 +16,7 @@
 # You should have received a copy of the GNU Lesser General Public License
 # along with IfcOpenShell.  If not, see <http://www.gnu.org/licenses/>.
 
+import pytest
 import test.bootstrap
 import ifcopenshell.api
 import ifcopenshell.util.classification
@@ -23,85 +24,127 @@ import ifcopenshell.util.classification
 
 class TestAddReference(test.bootstrap.IFC4):
     def test_adding_a_reference(self):
+        is_ifc2x3 = self.file.schema == "IFC2X3"
+
         ifcopenshell.api.run("root.create_entity", self.file, ifc_class="IfcProject")
         element = ifcopenshell.api.run("root.create_entity", self.file, ifc_class="IfcWall")
+        element2 = ifcopenshell.api.run("root.create_entity", self.file, ifc_class="IfcWall")
         result = ifcopenshell.api.run("classification.add_classification", self.file, classification="Name")
         ifcopenshell.api.run(
             "classification.add_reference",
             self.file,
-            product=element,
+            products=[element, element2],
             identification="X",
             name="Foobar",
             classification=result,
         )
         references = list(ifcopenshell.util.classification.get_references(element))
         assert len(references) == 1
-        assert references[0].Identification == "X"
+        assert getattr(references[0], "ItemReference" if is_ifc2x3 else "Identification") == "X"
         assert references[0].Name == "Foobar"
         assert references[0].ReferencedSource == self.file.by_type("IfcClassification")[0]
 
-        element2 = ifcopenshell.api.run("root.create_entity", self.file, ifc_class="IfcWall")
-        ifcopenshell.api.run(
-            "classification.add_reference",
-            self.file,
-            product=element2,
-            identification="X",
-            name="Foobar",
-            classification=result,
+        references2 = list(ifcopenshell.util.classification.get_references(element))
+        assert len(references2) == 1
+        assert getattr(references2[0], "ItemReference" if is_ifc2x3 else "Identification") == "X"
+        assert references2[0].Name == "Foobar"
+        assert references2[0] == references[0]
+
+        rel = next(
+            rel
+            for rel in self.file.by_type("IfcRelAssociatesClassification")
+            if rel.RelatingClassification == references[0]
         )
-        assert list(ifcopenshell.util.classification.get_references(element2))[0].Identification == "X"
-        assert list(ifcopenshell.util.classification.get_references(element2))[0].Name == "Foobar"
-        assert list(ifcopenshell.util.classification.get_references(element2))[0] == references[0]
+        assert len(rel.RelatedObjects) == 2
 
     def test_adding_a_library_based_reference(self):
+        is_ifc2x3 = self.file.schema == "IFC2X3"
+
         library = ifcopenshell.file()
         classification = library.createIfcClassification(Name="Name")
         reference = library.createIfcClassificationReference(Identification="1", ReferencedSource=classification)
 
         ifcopenshell.api.run("root.create_entity", self.file, ifc_class="IfcProject")
         element = ifcopenshell.api.run("root.create_entity", self.file, ifc_class="IfcWall")
+        element2 = ifcopenshell.api.run("root.create_entity", self.file, ifc_class="IfcWall")
         result = ifcopenshell.api.run("classification.add_classification", self.file, classification=classification)
         ifcopenshell.api.run(
             "classification.add_reference",
             self.file,
-            product=element,
+            products=[element, element2],
             reference=reference,
             classification=result,
         )
         references = list(ifcopenshell.util.classification.get_references(element))
         assert len(references) == 1
-        assert references[0].Identification == "1"
+        assert getattr(references[0], "ItemReference" if is_ifc2x3 else "Identification") == "1"
         assert references[0].ReferencedSource == self.file.by_type("IfcClassification")[0]
 
-    def test_adding_a_reference_to_a_resource(self):
+        references2 = list(ifcopenshell.util.classification.get_references(element2))
+        assert len(references2) == 1
+        assert getattr(references2[0], "ItemReference" if is_ifc2x3 else "Identification") == "1"
+        assert references2[0].ReferencedSource == self.file.by_type("IfcClassification")[0]
+        assert references[0] == references2[0]
+
+        rel = next(
+            rel
+            for rel in self.file.by_type("IfcRelAssociatesClassification")
+            if rel.RelatingClassification == references[0]
+        )
+        assert len(rel.RelatedObjects) == 2
+
+    def test_adding_a_reference_to_a_resource_and_to_a_root(self):
         ifcopenshell.api.run("root.create_entity", self.file, ifc_class="IfcProject")
         element = self.file.createIfcMaterial()
+        element2 = self.file.createIfcCostValue()
+        element3 = ifcopenshell.api.run("root.create_entity", self.file, ifc_class="IfcWall")
         result = ifcopenshell.api.run("classification.add_classification", self.file, classification="Name")
-        ifcopenshell.api.run(
-            "classification.add_reference",
-            self.file,
-            product=element,
-            identification="X",
-            name="Foobar",
-            classification=result,
-        )
+
+        if self.file.schema == "IFC2X3":
+            with pytest.raises(TypeError):
+                ifcopenshell.api.run(
+                    "classification.add_reference",
+                    self.file,
+                    products=[element, element2, element3],
+                    identification="X",
+                    name="Foobar",
+                    classification=result,
+                )
+            return
+        else:
+            ifcopenshell.api.run(
+                "classification.add_reference",
+                self.file,
+                products=[element, element2, element3],
+                identification="X",
+                name="Foobar",
+                classification=result,
+            )
+
         references = list(ifcopenshell.util.classification.get_references(element))
         assert len(references) == 1
         assert references[0].Identification == "X"
         assert references[0].Name == "Foobar"
         assert references[0].ReferencedSource == self.file.by_type("IfcClassification")[0]
 
-        element2 = self.file.createIfcCostValue()
-        ifcopenshell.api.run(
-            "classification.add_reference",
-            self.file,
-            product=element2,
-            identification="X",
-            name="Foobar",
-            classification=result,
-        )
-        assert list(ifcopenshell.util.classification.get_references(element2))[0].Identification == "X"
-        assert list(ifcopenshell.util.classification.get_references(element2))[0].Name == "Foobar"
-        assert list(ifcopenshell.util.classification.get_references(element2))[0] == references[0]
+        references2 = list(ifcopenshell.util.classification.get_references(element2))
+        assert references2[0].Identification == "X"
+        assert references2[0].Name == "Foobar"
+        assert references2[0] == references[0]
+
+        references3 = list(ifcopenshell.util.classification.get_references(element3))
+        assert references3[0].Identification == "X"
+        assert references3[0].Name == "Foobar"
+        assert references3[0] == references[0]
 
         assert len(self.file.by_type("IfcExternalReferenceRelationship")[0].RelatedResourceObjects) == 2
+        rel = next(
+            rel
+            for rel in self.file.by_type("IfcRelAssociatesClassification")
+            if rel.RelatingClassification == references[0]
+        )
+        assert len(rel.RelatedObjects) == 1
+
+
+class TestAddReferenceIFC2X3(test.bootstrap.IFC2X3, TestAddReference):
+    pass
diff --git a/src/ifcopenshell-python/test/api/classification/test_remove_classification.py b/src/ifcopenshell-python/test/api/classification/test_remove_classification.py
index 3652d6e8c8..fb3537ddf2 100644
--- a/src/ifcopenshell-python/test/api/classification/test_remove_classification.py
+++ b/src/ifcopenshell-python/test/api/classification/test_remove_classification.py
@@ -34,7 +34,7 @@ class TestRemoveClassification(test.bootstrap.IFC4):
         ifcopenshell.api.run(
             "classification.add_reference",
             self.file,
-            product=element,
+            products=[element],
             identification="X",
             name="Foobar",
             classification=result,
@@ -51,7 +51,7 @@ class TestRemoveClassification(test.bootstrap.IFC4):
         ifcopenshell.api.run(
             "classification.add_reference",
             self.file,
-            product=element,
+            products=[element],
             identification="X",
             name="Foobar",
             classification=result,
diff --git a/src/ifcopenshell-python/test/api/classification/test_remove_reference.py b/src/ifcopenshell-python/test/api/classification/test_remove_reference.py
index 597317f3bb..63ae287aa3 100644
--- a/src/ifcopenshell-python/test/api/classification/test_remove_reference.py
+++ b/src/ifcopenshell-python/test/api/classification/test_remove_reference.py
@@ -29,7 +29,7 @@ class TestRemoveReference(test.bootstrap.IFC4):
         reference = ifcopenshell.api.run(
             "classification.add_reference",
             self.file,
-            product=element,
+            products=[element],
             identification="X",
             name="Foobar",
             classification=result,
@@ -45,7 +45,7 @@ class TestRemoveReference(test.bootstrap.IFC4):
         reference = ifcopenshell.api.run(
             "classification.add_reference",
             self.file,
-            product=element,
+            products=[element],
             identification="X",
             name="Foobar",
             classification=result,
@@ -62,7 +62,7 @@ class TestRemoveReference(test.bootstrap.IFC4):
         reference = ifcopenshell.api.run(
             "classification.add_reference",
             self.file,
-            product=element,
+            products=[element],
             identification="X",
             name="Foobar",
             classification=result,
@@ -70,7 +70,7 @@ class TestRemoveReference(test.bootstrap.IFC4):
         reference2 = ifcopenshell.api.run(
             "classification.add_reference",
             self.file,
-            product=element2,
+            products=[element2],
             identification="X",
             name="Foobar",
             classification=result,
diff --git a/src/ifcopenshell-python/test/api/test_api.py b/src/ifcopenshell-python/test/api/test_api.py
index 779d1238f2..7910cf9739 100644
--- a/src/ifcopenshell-python/test/api/test_api.py
+++ b/src/ifcopenshell-python/test/api/test_api.py
@@ -18,6 +18,7 @@
 
 import test.bootstrap
 import ifcopenshell.api
+import ifcopenshell.util.classification
 import ifcopenshell.util.element
 import ifcopenshell.util.system
 from datetime import datetime
@@ -186,3 +187,35 @@ class TestTemporarySupportForDeprecatedAPIArguments(test.bootstrap.IFC4):
         assert len(self.file.by_type("IfcRelAssociatesMaterial")) == 0
         assert len(self.file.by_type("IfcWall")) == 1
         assert len(self.file.by_type("IfcMaterial")) == 1
+
+    @deprecation_check
+    def test_adding_a_reference(self):
+        ifcopenshell.api.run("root.create_entity", self.file, ifc_class="IfcProject")
+        element = ifcopenshell.api.run("root.create_entity", self.file, ifc_class="IfcWall")
+        result = ifcopenshell.api.run("classification.add_classification", self.file, classification="Name")
+        ifcopenshell.api.run(
+            "classification.add_reference",
+            self.file,
+            product=element,
+            identification="X",
+            name="Foobar",
+            classification=result,
+        )
+        references = list(ifcopenshell.util.classification.get_references(element))
+        assert len(references) == 1
+        assert references[0].Identification == "X"
+        assert references[0].Name == "Foobar"
+        assert references[0].ReferencedSource == self.file.by_type("IfcClassification")[0]
+
+        element2 = ifcopenshell.api.run("root.create_entity", self.file, ifc_class="IfcWall")
+        ifcopenshell.api.run(
+            "classification.add_reference",
+            self.file,
+            product=element2,
+            identification="X",
+            name="Foobar",
+            classification=result,
+        )
+        assert list(ifcopenshell.util.classification.get_references(element2))[0].Identification == "X"
+        assert list(ifcopenshell.util.classification.get_references(element2))[0].Name == "Foobar"
+        assert list(ifcopenshell.util.classification.get_references(element2))[0] == references[0]
diff --git a/src/ifcopenshell-python/test/util/test_classification.py b/src/ifcopenshell-python/test/util/test_classification.py
index d394f8056b..7fe054e1e3 100644
--- a/src/ifcopenshell-python/test/util/test_classification.py
+++ b/src/ifcopenshell-python/test/util/test_classification.py
@@ -34,14 +34,14 @@ class TestGetReferences(test.bootstrap.IFC4):
         ifcopenshell.api.run(
             "classification.add_reference",
             self.file,
-            product=element,
+            products=[element],
             reference=reference1,
             classification=classification,
         )
         ifcopenshell.api.run(
             "classification.add_reference",
             self.file,
-            product=element,
+            products=[element],
             reference=reference2,
             classification=classification,
         )
@@ -54,7 +54,7 @@ class TestGetReferences(test.bootstrap.IFC4):
         ifcopenshell.api.run(
             "classification.add_reference",
             self.file,
-            product=element,
+            products=[element],
             identification="X",
             name="Foobar",
             classification=result,
@@ -74,14 +74,14 @@ class TestGetReferences(test.bootstrap.IFC4):
         ifcopenshell.api.run(
             "classification.add_reference",
             self.file,
-            product=element,
+            products=[element],
             reference=reference1,
             classification=classification,
         )
         ifcopenshell.api.run(
             "classification.add_reference",
             self.file,
-            product=element_type,
+            products=[element_type],
             reference=reference2,
             classification=classification,
         )
@@ -103,14 +103,14 @@ class TestGetReferences(test.bootstrap.IFC4):
         ifcopenshell.api.run(
             "classification.add_reference",
             self.file,
-            product=element,
+            products=[element],
             reference=reference1,
             classification=classification,
         )
         ifcopenshell.api.run(
             "classification.add_reference",
             self.file,
-            product=element_type,
+            products=[element_type],
             reference=reference2,
             classification=classification,
         )
diff --git a/src/ifcopenshell-python/test/util/test_selector.py b/src/ifcopenshell-python/test/util/test_selector.py
index d8ba4bb174..571511d39f 100644
--- a/src/ifcopenshell-python/test/util/test_selector.py
+++ b/src/ifcopenshell-python/test/util/test_selector.py
@@ -225,7 +225,7 @@ class TestFilterElements(test.bootstrap.IFC4):
         ifcopenshell.api.run(
             "classification.add_reference",
             self.file,
-            product=element,
+            products=[element],
             identification="X",
             name="Foobar",
             classification=result,
diff --git a/src/ifctester/test/test_facet.py b/src/ifctester/test/test_facet.py
index bd89a00946..ddee91ab36 100644
--- a/src/ifctester/test/test_facet.py
+++ b/src/ifctester/test/test_facet.py
@@ -706,24 +706,24 @@ class TestClassification:
         element0 = ifcopenshell.api.run("root.create_entity", ifc, ifc_class="IfcWall")
         element1 = ifcopenshell.api.run("root.create_entity", ifc, ifc_class="IfcSlab")
         ifcopenshell.api.run(
-            "classification.add_reference", ifc, product=element1, reference=ref1, classification=system_a
+            "classification.add_reference", ifc, products=[element1], reference=ref1, classification=system_a
         )
         element11 = ifcopenshell.api.run("root.create_entity", ifc, ifc_class="IfcColumn")
         ifcopenshell.api.run(
-            "classification.add_reference", ifc, product=element11, reference=ref11, classification=system_a
+            "classification.add_reference", ifc, products=[element11], reference=ref11, classification=system_a
         )
         element22 = ifcopenshell.api.run("root.create_entity", ifc, ifc_class="IfcBeam")
         ifcopenshell.api.run(
             "classification.add_reference",
             ifc,
-            product=element22,
+            products=[element22],
             reference=ref22,
             classification=system_a,
             is_lightweight=False,
         )
         material = ifc.createIfcMaterial(Name="Material")
         ifcopenshell.api.run(
-            "classification.add_reference", ifc, product=material, reference=ref1, classification=system_a
+            "classification.add_reference", ifc, products=[material], reference=ref1, classification=system_a
         )
 
         facet = Classification(system="Foobar")
@@ -810,15 +810,15 @@ class TestClassification:
         wall_type = ifcopenshell.api.run("root.create_entity", ifc, ifc_class="IfcWallType")
         ifcopenshell.api.run("type.assign_type", ifc, related_objects=[wall], relating_type=wall_type)
         ifcopenshell.api.run(
-            "classification.add_reference", ifc, product=wall, reference=ref11, classification=system_a
+            "classification.add_reference", ifc, products=[wall], reference=ref11, classification=system_a
         )
         ifcopenshell.api.run(
-            "classification.add_reference", ifc, product=wall_type, reference=ref22, classification=system_a
+            "classification.add_reference", ifc, products=[wall_type], reference=ref22, classification=system_a
         )
 
         system_b = ifcopenshell.api.run("classification.add_classification", ifc, classification=system_b)
         ifcopenshell.api.run(
-            "classification.add_reference", ifc, product=wall_type, reference=refx, classification=system_b
+            "classification.add_reference", ifc, products=[wall_type], reference=refx, classification=system_b
         )
 
         facet = Classification(system="Foobar", value="11")