diff --git a/src/pynwb/testing/mock/file.py b/src/pynwb/testing/mock/file.py
index 943f86dcb..351f81454 100644
--- a/src/pynwb/testing/mock/file.py
+++ b/src/pynwb/testing/mock/file.py
@@ -1,7 +1,7 @@
 from typing import Optional
 from uuid import uuid4
 from datetime import datetime
-from dateutil.tz import tzlocal
+from dateutil.tz import tzutc
 
 from ...file import NWBFile, Subject
 from .utils import name_generator
@@ -10,7 +10,7 @@
 def mock_NWBFile(
     session_description: str = 'session_description',
     identifier: Optional[str] = None,
-    session_start_time: datetime = datetime(1970, 1, 1, tzinfo=tzlocal()),
+    session_start_time: datetime = datetime(1970, 1, 1, tzinfo=tzutc()),
     **kwargs
 ):
     return NWBFile(