diff --git a/auth.go b/auth.go
index 1da99813..b85bae17 100644
--- a/auth.go
+++ b/auth.go
@@ -180,7 +180,7 @@ func filterDefinition(sourceSchema *ast.Schema, visited map[string]bool, types m
 				// Node interface is not defined in the merged schema
 				continue
 			}
-			if typ.Kind == ast.Interface {
+			if typ.IsAbstractType() {
 				for _, pt := range sourceSchema.PossibleTypes[typ.Name] {
 					types[pt.Name] = pt
 					_ = filterDefinition(sourceSchema, visited, types, pt, AllowedFields{AllowAll: true})
@@ -194,12 +194,6 @@ func filterDefinition(sourceSchema *ast.Schema, visited map[string]bool, types m
 			_ = filterDefinition(sourceSchema, visited, types, sourceSchema.Types[typeName], AllowedFields{AllowAll: true})
 		}
 
-		// unions
-		for _, t := range def.Types {
-			types[t] = sourceSchema.Types[t]
-			_ = filterDefinition(sourceSchema, visited, types, sourceSchema.Types[t], AllowedFields{AllowAll: true})
-		}
-
 		return &resDef
 	}
 
@@ -212,8 +206,8 @@ func filterDefinition(sourceSchema *ast.Schema, visited map[string]bool, types m
 				// Node interface is not defined in the merged schema
 				continue
 			}
-			// if the type is an interface we filter all the possible types
-			if typ.Kind == ast.Interface {
+			// if the type is abstract we filter all the possible types
+			if typ.IsAbstractType() {
 				for _, pt := range sourceSchema.PossibleTypes[typ.Name] {
 					newTypeDef := filterDefinition(sourceSchema, visited, types, pt, allowedSubFields)
 					if typeDef, ok := types[pt.Name]; ok {
diff --git a/auth_test.go b/auth_test.go
index 6428b10a..2b9b367b 100644
--- a/auth_test.go
+++ b/auth_test.go
@@ -421,7 +421,7 @@ func TestFilterSchema(t *testing.T) {
 		`), formatSchema(filteredSchema))
 	})
 
-	t.Run(`union`, func(t *testing.T) {
+	t.Run(`union, allow all`, func(t *testing.T) {
 		perms := OperationPermissions{
 			AllowedRootQueryFields: AllowedFields{AllowedSubfields: map[string]AllowedFields{
 				"somethingRandom": {
@@ -454,6 +454,35 @@ func TestFilterSchema(t *testing.T) {
 		`), formatSchema(filteredSchema))
 	})
 
+	t.Run(`union`, func(t *testing.T) {
+		perms := OperationPermissions{
+			AllowedRootQueryFields: AllowedFields{AllowedSubfields: map[string]AllowedFields{
+				"somethingRandom": {
+					AllowedSubfields: map[string]AllowedFields{
+						"id": {},
+					},
+				},
+			},
+			},
+		}
+		filteredSchema := perms.FilterSchema(schema)
+		assert.Equal(t, loadAndFormatSchema(`
+			union MovieOrCinema = Movie | Cinema
+
+			type Cinema {
+				id: ID!
+			}
+
+			type Movie {
+				id: ID!
+			}
+
+			type Query {
+				somethingRandom: MovieOrCinema!
+			}
+		`), formatSchema(filteredSchema))
+	})
+
 	t.Run(`interface`, func(t *testing.T) {
 		perms := OperationPermissions{
 			AllowedRootQueryFields: AllowedFields{AllowedSubfields: map[string]AllowedFields{