diff --git a/handwritten/firestore/dev/system-test/pipeline.ts b/handwritten/firestore/dev/system-test/pipeline.ts
index 8377424c8d2..2937ce02e9b 100644
--- a/handwritten/firestore/dev/system-test/pipeline.ts
+++ b/handwritten/firestore/dev/system-test/pipeline.ts
@@ -2072,6 +2072,34 @@ describe.skipClassic('Pipeline class', () => {
         );
       });
 
+      it('run pipeline with user data with union', async () => {
+        const snapshot = await firestore
+          .pipeline()
+          .collection(randomCol.path)
+          .union(
+            firestore
+              .pipeline()
+              .collection(randomCol.path)
+              .where(equal('title', "The Hitchhiker's Guide to the Galaxy")),
+          )
+          .sort(field(FieldPath.documentId()).ascending())
+          .execute();
+        expectResults(
+          snapshot,
+          'book1',
+          'book1',
+          'book10',
+          'book2',
+          'book3',
+          'book4',
+          'book5',
+          'book6',
+          'book7',
+          'book8',
+          'book9',
+        );
+      });
+
       it('supports options', async () => {
         const snapshot = await firestore
           .pipeline()