diff --git a/backend/app/api/endpoints/maintenance_schedules.py b/backend/app/api/endpoints/maintenance_schedules.py
index b1703dd9..df427082 100644
--- a/backend/app/api/endpoints/maintenance_schedules.py
+++ b/backend/app/api/endpoints/maintenance_schedules.py
@@ -10,6 +10,7 @@ import pytz
 
 from app.api.deps import get_current_active_user, get_db
 from app.models.maintenance_schedule import MaintenanceSchedule
+from app.models.tree import Tree
 from app.models.user import User
 from app.schemas.maintenance_schedule import (
     MaintenanceScheduleCreate,
@@ -28,6 +29,19 @@ def _compute_next_run(cron_expression: str, tz_name: str) -> datetime:
     return cron.get_next(datetime).astimezone(timezone.utc)
 
 
+async def _get_tree_or_403(tree_id: UUID, current_user: User, db: AsyncSession) -> "Tree":
+    """Fetch tree and verify the current user's team owns it."""
+    result = await db.execute(select(Tree).where(Tree.id == tree_id))
+    tree = result.scalar_one_or_none()
+    if not tree:
+        raise HTTPException(status_code=404, detail="Tree not found")
+    # Super admins can access any tree; regular users must be on the same team
+    if not getattr(current_user, 'is_super_admin', False):
+        if tree.team_id != current_user.team_id:
+            raise HTTPException(status_code=403, detail="Access denied")
+    return tree
+
+
 @router.post("", response_model=MaintenanceScheduleResponse, status_code=201)
 async def create_schedule(
     data: MaintenanceScheduleCreate,
@@ -35,6 +49,9 @@ async def create_schedule(
     db: Annotated[AsyncSession, Depends(get_db)],
 ):
     """Create a cron schedule for a maintenance flow. One per flow."""
+    # Verify user's team owns the tree
+    await _get_tree_or_403(data.tree_id, current_user, db)
+
     # Check no existing schedule for this tree
     existing = await db.execute(
         select(MaintenanceSchedule).where(MaintenanceSchedule.tree_id == data.tree_id)
@@ -69,6 +86,9 @@ async def get_schedule_for_tree(
     db: Annotated[AsyncSession, Depends(get_db)],
 ):
     """Get the schedule for a specific maintenance flow."""
+    # Verify user's team owns the tree before returning schedule data
+    await _get_tree_or_403(tree_id, current_user, db)
+
     result = await db.execute(
         select(MaintenanceSchedule).where(MaintenanceSchedule.tree_id == tree_id)
     )
@@ -93,6 +113,9 @@ async def update_schedule(
     if not schedule:
         raise HTTPException(status_code=404, detail="Schedule not found")
 
+    # Verify user's team owns the tree this schedule belongs to
+    await _get_tree_or_403(schedule.tree_id, current_user, db)
+
     update_fields = data.model_fields_set
     if "cron_expression" in update_fields and data.cron_expression is not None:
         schedule.cron_expression = data.cron_expression
diff --git a/backend/tests/test_maintenance_schedules.py b/backend/tests/test_maintenance_schedules.py
index 954339c4..32c5666d 100644
--- a/backend/tests/test_maintenance_schedules.py
+++ b/backend/tests/test_maintenance_schedules.py
@@ -96,3 +96,45 @@ async def test_get_schedule_not_found(client: AsyncClient, auth_headers: dict):
     tree_id = await _create_maintenance_tree(client, auth_headers)
     resp = await client.get(f"/api/v1/maintenance-schedules/tree/{tree_id}", headers=auth_headers)
     assert resp.status_code == 404
+
+
+@pytest.mark.asyncio
+async def test_cannot_schedule_other_teams_tree(client: AsyncClient, auth_headers: dict, test_db):
+    """User cannot create a schedule for a tree belonging to another team."""
+    import uuid as _uuid
+    from app.models.team import Team
+    from app.models.tree import Tree
+
+    # Create a tree belonging to a DIFFERENT team directly in DB
+    other_team = Team(name=f"Other Team {_uuid.uuid4()}")
+    test_db.add(other_team)
+    await test_db.flush()
+
+    other_tree = Tree(
+        name="Other Team Tree",
+        tree_type="maintenance",
+        team_id=other_team.id,
+        tree_structure={
+            "steps": [
+                {"id": "s1", "type": "procedure_step", "title": "Step",
+                 "description": "Do it", "content_type": "action"},
+                {"id": "end", "type": "procedure_end", "title": "Done"},
+            ]
+        },
+        status="published",
+        visibility="team",
+    )
+    test_db.add(other_tree)
+    await test_db.flush()
+
+    # Current user (from auth_headers) tries to schedule it
+    resp = await client.post(
+        "/api/v1/maintenance-schedules",
+        json={
+            "tree_id": str(other_tree.id),
+            "cron_expression": "0 9 1 * *",
+            "timezone": "UTC",
+        },
+        headers=auth_headers,
+    )
+    assert resp.status_code in (403, 404)  # either is acceptable