diff --git a/internal/webhooks/notification/v1alpha1/contactgroupmembership_webhook.go b/internal/webhooks/notification/v1alpha1/contactgroupmembership_webhook.go
index 38823d44..0faf296d 100644
--- a/internal/webhooks/notification/v1alpha1/contactgroupmembership_webhook.go
+++ b/internal/webhooks/notification/v1alpha1/contactgroupmembership_webhook.go
@@ -109,6 +109,19 @@ func (v *ContactGroupMembershipValidator) ValidateCreate(ctx context.Context, ob
 		errs = append(errs, field.Invalid(field.NewPath("spec"), cgm.Spec, fmt.Sprintf("cannot create membership as a ContactGroupMembershipRemoval %s already exists", existingRemovals.Items[0].Name)))
 	}
 
+	// Check that cgm namespace is the same as the contact namespace for contacts that are related
+	// to the resourcemanager.miloapis.com API group
+	if contact.Spec.SubjectRef != nil {
+		switch contact.Spec.SubjectRef.APIGroup {
+		case "resourcemanager.miloapis.com":
+			if cgm.Namespace != contact.Namespace {
+				errs = append(errs, field.Invalid(field.NewPath("spec"), cgm.Spec, "namespace must be the same as the contact namespace for contacts that are related to the resourcemanager.miloapis.com API group"))
+			}
+		default:
+			return nil, errors.NewInternalError(fmt.Errorf("server does not handle SubjectRef APIGroup %s", contact.Spec.SubjectRef.APIGroup))
+		}
+	}
+
 	if len(errs) > 0 {
 		return nil, errors.NewInvalid(notificationv1alpha1.SchemeGroupVersion.WithKind("ContactGroupMembership").GroupKind(), cgm.Name, errs)
 	}
diff --git a/internal/webhooks/notification/v1alpha1/contactgroupmembership_webhook_test.go b/internal/webhooks/notification/v1alpha1/contactgroupmembership_webhook_test.go
index 2841cc3d..d8f6371e 100644
--- a/internal/webhooks/notification/v1alpha1/contactgroupmembership_webhook_test.go
+++ b/internal/webhooks/notification/v1alpha1/contactgroupmembership_webhook_test.go
@@ -104,6 +104,45 @@ func TestContactGroupMembershipValidator(t *testing.T) {
 			expectError:   true,
 			errorContains: "not found",
 		},
+		"subjectref same namespace": {
+			newObj: &notificationv1alpha1.ContactGroupMembership{
+				ObjectMeta: metav1.ObjectMeta{Name: "m6", Namespace: "default"},
+				Spec: notificationv1alpha1.ContactGroupMembershipSpec{
+					ContactRef:      notificationv1alpha1.ContactReference{Name: "c-sub", Namespace: "default"},
+					ContactGroupRef: notificationv1alpha1.ContactGroupReference{Name: "g-sub", Namespace: "default"},
+				},
+			},
+			seedObjects: []client.Object{
+				&notificationv1alpha1.Contact{
+					ObjectMeta: metav1.ObjectMeta{Name: "c-sub", Namespace: "default"},
+					Spec: notificationv1alpha1.ContactSpec{
+						SubjectRef: &notificationv1alpha1.SubjectReference{APIGroup: "resourcemanager.miloapis.com", Kind: "Project", Name: "proj1"},
+					},
+				},
+				&notificationv1alpha1.ContactGroup{ObjectMeta: metav1.ObjectMeta{Name: "g-sub", Namespace: "default"}},
+			},
+			expectError: false,
+		},
+		"subjectref namespace mismatch": {
+			newObj: &notificationv1alpha1.ContactGroupMembership{
+				ObjectMeta: metav1.ObjectMeta{Name: "m7", Namespace: "other"},
+				Spec: notificationv1alpha1.ContactGroupMembershipSpec{
+					ContactRef:      notificationv1alpha1.ContactReference{Name: "c-sub", Namespace: "default"},
+					ContactGroupRef: notificationv1alpha1.ContactGroupReference{Name: "g-sub", Namespace: "other"},
+				},
+			},
+			seedObjects: []client.Object{
+				&notificationv1alpha1.Contact{
+					ObjectMeta: metav1.ObjectMeta{Name: "c-sub", Namespace: "default"},
+					Spec: notificationv1alpha1.ContactSpec{
+						SubjectRef: &notificationv1alpha1.SubjectReference{APIGroup: "resourcemanager.miloapis.com", Kind: "Project", Name: "proj1"},
+					},
+				},
+				&notificationv1alpha1.ContactGroup{ObjectMeta: metav1.ObjectMeta{Name: "g-sub", Namespace: "other"}},
+			},
+			expectError:   true,
+			errorContains: "namespace must be the same",
+		},
 	}
 
 	for name, tt := range tests {
diff --git a/internal/webhooks/notification/v1alpha1/contactgroupmembershipremoval_webhook.go b/internal/webhooks/notification/v1alpha1/contactgroupmembershipremoval_webhook.go
index 7f86650f..3d318879 100644
--- a/internal/webhooks/notification/v1alpha1/contactgroupmembershipremoval_webhook.go
+++ b/internal/webhooks/notification/v1alpha1/contactgroupmembershipremoval_webhook.go
@@ -50,7 +50,8 @@ func (v *ContactGroupMembershipRemovalValidator) ValidateCreate(ctx context.Cont
 	var errs field.ErrorList
 
 	// Ensure Contact exists
-	if err := v.Client.Get(ctx, client.ObjectKey{Namespace: removal.Spec.ContactRef.Namespace, Name: removal.Spec.ContactRef.Name}, &notificationv1alpha1.Contact{}); err != nil {
+	contact := &notificationv1alpha1.Contact{}
+	if err := v.Client.Get(ctx, client.ObjectKey{Namespace: removal.Spec.ContactRef.Namespace, Name: removal.Spec.ContactRef.Name}, contact); err != nil {
 		if errors.IsNotFound(err) {
 			errs = append(errs, field.NotFound(field.NewPath("spec", "contactRef", "name"), removal.Spec.ContactRef.Name))
 		} else {
@@ -79,6 +80,19 @@ func (v *ContactGroupMembershipRemovalValidator) ValidateCreate(ctx context.Cont
 		errs = append(errs, field.Duplicate(field.NewPath("spec"), fmt.Sprintf("membership removal already exists in ContactGroupMembershipRemoval %s", existing.Items[0].Name)))
 	}
 
+	// Check that cgmr namespace is the same as the contact namespace for contacts that are related
+	// to the resourcemanager.miloapis.com API group
+	if contact.Spec.SubjectRef != nil {
+		switch contact.Spec.SubjectRef.APIGroup {
+		case "resourcemanager.miloapis.com":
+			if removal.Namespace != contact.Namespace {
+				errs = append(errs, field.Invalid(field.NewPath("spec"), removal.Spec, "namespace must be the same as the contact namespace for contacts that are related to the resourcemanager.miloapis.com API group"))
+			}
+		default:
+			return nil, errors.NewInternalError(fmt.Errorf("server does not handle SubjectRef APIGroup %s", contact.Spec.SubjectRef.APIGroup))
+		}
+	}
+
 	if len(errs) > 0 {
 		return nil, errors.NewInvalid(notificationv1alpha1.SchemeGroupVersion.WithKind("ContactGroupMembershipRemoval").GroupKind(), removal.Name, errs)
 	}
diff --git a/internal/webhooks/notification/v1alpha1/contactgroupmembershipremoval_webhook_test.go b/internal/webhooks/notification/v1alpha1/contactgroupmembershipremoval_webhook_test.go
index 9482b6c8..56004d48 100644
--- a/internal/webhooks/notification/v1alpha1/contactgroupmembershipremoval_webhook_test.go
+++ b/internal/webhooks/notification/v1alpha1/contactgroupmembershipremoval_webhook_test.go
@@ -37,6 +37,24 @@ func TestContactGroupMembershipRemovalValidator(t *testing.T) {
 		return &notificationv1alpha1.ContactGroup{ObjectMeta: metav1.ObjectMeta{Name: name, Namespace: "default"}}
 	}
 
+	// makeContactWithSubject creates a Contact that includes a SubjectRef with the given apiGroup and namespace.
+	makeContactWithSubject := func(name, ns, apiGroup string) *notificationv1alpha1.Contact {
+		return &notificationv1alpha1.Contact{
+			ObjectMeta: metav1.ObjectMeta{Name: name, Namespace: ns},
+			Spec: notificationv1alpha1.ContactSpec{
+				SubjectRef: &notificationv1alpha1.SubjectReference{
+					APIGroup:  apiGroup,
+					Kind:      "User",
+					Name:      "demo", // value not relevant for validator logic
+					Namespace: ns,
+				},
+				FamilyName: "Doe",
+				GivenName:  "John",
+				Email:      "john.doe@example.com",
+			},
+		}
+	}
+
 	tests := map[string]struct {
 		newObj        *notificationv1alpha1.ContactGroupMembershipRemoval
 		seedObjects   []client.Object
@@ -81,6 +99,29 @@ func TestContactGroupMembershipRemovalValidator(t *testing.T) {
 			},
 			expectError: false,
 		},
+		"contact with resourcemanager apiGroup same namespace": {
+			newObj:      makeRemoval("rm7", "c-res", "g1"),
+			seedObjects: []client.Object{makeContactWithSubject("c-res", "default", "resourcemanager.miloapis.com"), makeGroup("g1")},
+			expectError: false,
+		},
+		"contact with resourcemanager apiGroup different namespace": {
+			newObj: &notificationv1alpha1.ContactGroupMembershipRemoval{
+				ObjectMeta: metav1.ObjectMeta{Name: "rm8", Namespace: "other-ns"},
+				Spec: notificationv1alpha1.ContactGroupMembershipRemovalSpec{
+					ContactRef:      notificationv1alpha1.ContactReference{Name: "c-res", Namespace: "default"},
+					ContactGroupRef: notificationv1alpha1.ContactGroupReference{Name: "g1", Namespace: "default"},
+				},
+			},
+			seedObjects:   []client.Object{makeContactWithSubject("c-res", "default", "resourcemanager.miloapis.com"), makeGroup("g1")},
+			expectError:   true,
+			errorContains: "namespace must be the same",
+		},
+		"contact with unsupported apiGroup": {
+			newObj:        makeRemoval("rm9", "c-oth", "g1"),
+			seedObjects:   []client.Object{makeContactWithSubject("c-oth", "default", "unsupported.group"), makeGroup("g1")},
+			expectError:   true,
+			errorContains: "server does not handle subjectref apigroup",
+		},
 	}
 
 	for name, tt := range tests {