diff --git a/atst/domain/task_orders.py b/atst/domain/task_orders.py
index 9ecf41e9..38527d17 100644
--- a/atst/domain/task_orders.py
+++ b/atst/domain/task_orders.py
@@ -1,4 +1,5 @@
 import datetime
+from sqlalchemy import or_
 
 from atst.database import db
 from atst.models.clin import CLIN
@@ -76,3 +77,17 @@ class TaskOrders(BaseDomainClass):
         task_order = TaskOrders.get(task_order_id)
         db.session.delete(task_order)
         db.session.commit()
+
+    @classmethod
+    def get_for_send_task_order_files(cls):
+        return (
+            db.session.query(TaskOrder)
+            .join(CLIN)
+            .filter(
+                or_(
+                    TaskOrder.pdf_last_sent_at < CLIN.last_sent_at,
+                    TaskOrder.pdf_last_sent_at.is_(None),
+                )
+            )
+            .all()
+        )
diff --git a/tests/domain/test_task_orders.py b/tests/domain/test_task_orders.py
index 42da74e6..2db84c5c 100644
--- a/tests/domain/test_task_orders.py
+++ b/tests/domain/test_task_orders.py
@@ -1,5 +1,5 @@
 import pytest
-from datetime import date, timedelta
+from datetime import date, datetime, timedelta
 from decimal import Decimal
 
 from atst.domain.exceptions import AlreadyExistsError
@@ -178,3 +178,21 @@ def test_allows_alphanumeric_number():
 
     for number in valid_to_numbers:
         assert TaskOrders.create(portfolio.id, number, [], None)
+
+
+def test_get_for_send_task_order_files():
+    new_to = TaskOrderFactory.create(create_clins=[{}])
+    updated_to = TaskOrderFactory.create(
+        create_clins=[{"last_sent_at": datetime(2020, 2, 1)}],
+        pdf_last_sent_at=datetime(2020, 1, 1),
+    )
+    sent_to = TaskOrderFactory.create(
+        create_clins=[{"last_sent_at": datetime(2020, 1, 1)}],
+        pdf_last_sent_at=datetime(2020, 1, 1),
+    )
+
+    updated_and_new_task_orders = TaskOrders.get_for_send_task_order_files()
+    assert len(updated_and_new_task_orders) == 2
+    assert sent_to not in updated_and_new_task_orders
+    assert updated_to in updated_and_new_task_orders
+    assert new_to in updated_and_new_task_orders
diff --git a/tests/factories.py b/tests/factories.py
index b7a63243..aa0a986a 100644
--- a/tests/factories.py
+++ b/tests/factories.py
@@ -322,6 +322,7 @@ class TaskOrderFactory(Base):
     number = factory.LazyFunction(random_task_order_number)
     signed_at = None
     _pdf = factory.SubFactory(AttachmentFactory)
+    pdf_last_sent_at = None
 
     @classmethod
     def _create(cls, model_class, *args, **kwargs):
@@ -347,6 +348,7 @@ class CLINFactory(Base):
     jedi_clin_type = factory.LazyFunction(
         lambda *args: random.choice(list(clin.JEDICLINType))
     )
+    last_sent_at = None
 
 
 class NotificationRecipientFactory(Base):