diff --git a/alembic/versions/3bd8552f1c57_add_unique_constraint_to_task_order_.py b/alembic/versions/3bd8552f1c57_add_unique_constraint_to_task_order_.py
new file mode 100644
index 00000000..01794a93
--- /dev/null
+++ b/alembic/versions/3bd8552f1c57_add_unique_constraint_to_task_order_.py
@@ -0,0 +1,28 @@
+"""add unique constraint to task order number
+
+Revision ID: 3bd8552f1c57
+Revises: 67a2151d6269
+Create Date: 2019-12-10 12:45:17.535973
+
+"""
+from alembic import op
+import sqlalchemy as sa
+from sqlalchemy.dialects import postgresql
+
+# revision identifiers, used by Alembic.
+revision = '3bd8552f1c57' # pragma: allowlist secret
+down_revision = '67a2151d6269' # pragma: allowlist secret
+branch_labels = None
+depends_on = None
+
+
+def upgrade():
+    # ### commands auto generated by Alembic - please adjust! ###
+    op.create_unique_constraint(None, 'task_orders', ['number'])
+    # ### end Alembic commands ###
+
+
+def downgrade():
+    # ### commands auto generated by Alembic - please adjust! ###
+    op.drop_constraint(None, 'task_orders', type_='unique')
+    # ### end Alembic commands ###
diff --git a/atst/models/task_order.py b/atst/models/task_order.py
index 1a46e505..eba34147 100644
--- a/atst/models/task_order.py
+++ b/atst/models/task_order.py
@@ -39,7 +39,7 @@ class TaskOrder(Base, mixins.TimestampsMixin):
 
     pdf_attachment_id = Column(ForeignKey("attachments.id"))
     _pdf = relationship("Attachment", foreign_keys=[pdf_attachment_id])
-    number = Column(String)  # Task Order Number
+    number = Column(String, unique=True,)  # Task Order Number
     signer_dod_id = Column(String)
     signed_at = Column(DateTime)