diff --git a/SAS/TMSS/backend/src/tmss/tmssapp/subtasks.py b/SAS/TMSS/backend/src/tmss/tmssapp/subtasks.py
index 5a314a43ba3841a82c07079f0d44ae0c7db31c9e..7b1d1931bb25ca1dc9921429c3171b077d2afef9 100644
--- a/SAS/TMSS/backend/src/tmss/tmssapp/subtasks.py
+++ b/SAS/TMSS/backend/src/tmss/tmssapp/subtasks.py
@@ -1096,6 +1096,9 @@ def check_prerequities_for_scheduling(subtask: Subtask) -> bool:
     if subtask.state.value != SubtaskState.Choices.DEFINED.value:
         raise SubtaskSchedulingException("Cannot schedule subtask id=%d because it is not DEFINED. Current state=%s" % (subtask.pk, subtask.state.value))
 
+    if subtask.obsolete_since is not None:
+        raise SubtaskSchedulingException("Cannot schedule subtask id=%d because it is marked as obsolete since %s" % (subtask.pk, subtask.obsolete_since))
+
     for predecessor in subtask.predecessors.all():
         if predecessor.state.value != SubtaskState.Choices.FINISHED.value:
             raise SubtaskSchedulingException("Cannot schedule subtask id=%d because its predecessor id=%s in not FINISHED but state=%s"