diff --git a/litellm/integrations/gcs_pubsub/pub_sub.py b/litellm/integrations/gcs_pubsub/pub_sub.py
index bdaedcd9089..db7f9bb4d0b 100644
--- a/litellm/integrations/gcs_pubsub/pub_sub.py
+++ b/litellm/integrations/gcs_pubsub/pub_sub.py
@@ -75,7 +75,7 @@ class GcsPubSubLogger(CustomBatchLogger):
             vertex_project,
         ) = await vertex_chat_completion._ensure_access_token_async(
             credentials=self.path_service_account_json,
-            project_id=None,
+            project_id=self.project_id,
             custom_llm_provider="vertex_ai",
         )
 
diff --git a/tests/litellm/integrations/gcs_pubsub/test_pub_sub.py b/tests/litellm/integrations/gcs_pubsub/test_pub_sub.py
new file mode 100644
index 00000000000..7ff28bfe831
--- /dev/null
+++ b/tests/litellm/integrations/gcs_pubsub/test_pub_sub.py
@@ -0,0 +1,68 @@
+import datetime
+import json
+import os
+import sys
+import unittest
+from typing import List, Optional, Tuple
+from unittest.mock import ANY, MagicMock, Mock, patch
+
+import httpx
+import pytest
+
+sys.path.insert(
+    0, os.path.abspath("../../..")
+)  # Adds the parent directory to the system-path
+import litellm
+
+
+@pytest.mark.asyncio
+async def test_construct_request_headers_project_id_from_env(monkeypatch):
+    """Test that construct_request_headers uses GCS_PUBSUB_PROJECT_ID environment variable."""
+    from litellm.integrations.gcs_pubsub.pub_sub import GcsPubSubLogger
+
+    # Set up test environment variable
+    test_project_id = "test-project-123"
+    monkeypatch.setenv("GCS_PUBSUB_PROJECT_ID", test_project_id)
+    monkeypatch.setattr(
+        "litellm.proxy.proxy_server.premium_user",
+        True,
+    )
+
+    try:
+        # Create handler with no project_id
+        handler = GcsPubSubLogger(
+            topic_id="test-topic", credentials_path="test-path.json"
+        )
+
+        # Mock the Vertex AI auth calls
+        mock_auth_header = "mock-auth-header"
+        mock_token = "mock-token"
+
+        with patch(
+            "litellm.vertex_chat_completion._ensure_access_token_async"
+        ) as mock_ensure_token:
+            mock_ensure_token.return_value = (mock_auth_header, test_project_id)
+
+            with patch(
+                "litellm.vertex_chat_completion._get_token_and_url"
+            ) as mock_get_token:
+                mock_get_token.return_value = (mock_token, "mock-url")
+
+                # Call construct_request_headers
+                headers = await handler.construct_request_headers()
+
+                # Verify headers
+                assert headers == {
+                    "Authorization": f"Bearer {mock_token}",
+                    "Content-Type": "application/json",
+                }
+
+                # Verify _ensure_access_token_async was called with correct project_id
+                mock_ensure_token.assert_called_once_with(
+                    credentials="test-path.json",
+                    project_id=test_project_id,
+                    custom_llm_provider="vertex_ai",
+                )
+    finally:
+        # Clean up environment variable
+        del os.environ["GCS_PUBSUB_PROJECT_ID"]