diff --git a/xos/synchronizer/models/models.py b/xos/synchronizer/models/models.py
index 9431488..ed1e062 100644
--- a/xos/synchronizer/models/models.py
+++ b/xos/synchronizer/models/models.py
@@ -14,7 +14,6 @@
 
 import random
 
-from core.models.xosbase import *
 from xos.exceptions import XOSValidationError
 
 from models_decl import VOLTService_decl
@@ -36,16 +35,44 @@
         except IndexError, e:
             return False
 
-
 class VOLTServiceInstance(VOLTServiceInstance_decl):
     class Meta:
-        proxy = True 
-
+        proxy = True
 
 class OLTDevice(OLTDevice_decl):
     class Meta:
-        proxy = True 
+        proxy = True
 
+    def get_volt_si(self):
+        return VOLTServiceInstance.objects.all()
+
+    def delete(self, *args, **kwargs):
+
+        onus = []
+        pon_ports = self.pon_ports.all()
+        for port in pon_ports:
+            onus = onus + list(port.onu_devices.all())
+
+
+        if len(onus) > 0:
+            onus = [o.id for o in onus]
+
+            # find the ONUs used by VOLTServiceInstances
+            used_onus = [o.onu_device_id for o in self.get_volt_si()]
+
+            # find the intersection between the onus associated with this OLT and the used one
+            used_onus_to_delete = [o for o in onus if o in used_onus]
+
+            if len(used_onus_to_delete) > 0:
+                if hasattr(self, "device_id") and self.device_id:
+                    item = self.device_id
+                elif hasattr(self, "name") and self.name:
+                    item = self.name
+                else:
+                    item = self.id
+                raise XOSValidationError('OLT "%s" can\'t be deleted as it has subscribers associated with its ONUs' % item)
+
+        super(OLTDevice, self).delete(*args, **kwargs)
 
 class PONPort(PONPort_decl):
     class Meta:
diff --git a/xos/synchronizer/models/test_oltdevice_model.py b/xos/synchronizer/models/test_oltdevice_model.py
new file mode 100644
index 0000000..34bf200
--- /dev/null
+++ b/xos/synchronizer/models/test_oltdevice_model.py
@@ -0,0 +1,77 @@
+# Copyright 2017-present Open Networking Foundation
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+# http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import unittest
+from mock import patch, Mock, MagicMock
+
+# mocking XOS exception, as they're based in Django
+class Exceptions:
+    XOSValidationError = Exception
+
+class XOS:
+    exceptions = Exceptions
+
+class TestOLTDeviceModel(unittest.TestCase):
+    def setUp(self):
+        self.xos = XOS
+
+        self.models_decl = Mock()
+        self.models_decl.OLTDevice_decl = MagicMock
+        self.models_decl.OLTDevice_decl.delete = Mock()
+
+        modules = {
+            'xos.exceptions': self.xos.exceptions,
+            'models_decl': self.models_decl,
+        }
+
+        self.module_patcher = patch.dict('sys.modules', modules)
+        self.module_patcher.start()
+
+        from models import OLTDevice
+
+        print OLTDevice
+
+        self.olt_device = OLTDevice()
+        self.olt_device.id = None # this is a new model
+        self.olt_device.is_new = True
+        self.olt_device.device_id = 1234
+
+
+    def test_delete(self):
+        self.olt_device.delete()
+        self.models_decl.OLTDevice_decl.delete.assert_called()
+
+    def test_prevent_delete(self):
+
+        onu1 = Mock()
+        onu1.id = 1
+
+        pon1 = Mock()
+        pon1.onu_devices.all.return_value = [onu1]
+
+        self.olt_device.pon_ports.all.return_value = [pon1]
+
+        volt_si_1 = Mock()
+        volt_si_1.onu_device_id = onu1.id
+
+        with patch.object(self.olt_device, "get_volt_si")as volt_si_get:
+            volt_si_get.return_value = [volt_si_1]
+            with self.assertRaises(Exception) as e:
+                self.olt_device.delete()
+
+            self.assertEqual(e.exception.message, 'OLT "1234" can\'t be deleted as it has subscribers associated with its ONUs')
+            self.models_decl.OLTDevice_decl.delete.assert_not_called()
+
+if __name__ == '__main__':
+    unittest.main()
diff --git a/xos/synchronizer/models/volt.xproto b/xos/synchronizer/models/volt.xproto
index 0eda4e0..39383f4 100644
--- a/xos/synchronizer/models/volt.xproto
+++ b/xos/synchronizer/models/volt.xproto
@@ -16,14 +16,6 @@
     required string onos_voltha_pass = 8 [help_text = "The ONOS Voltha password. By default rocks", max_length = 254, default="rocks", null = True, db_index = False, blank = False];
 }
 
-message VOLTServiceInstance (ServiceInstance){
-    option kind = "vOLT";
-    option owner_class_name = "VOLTService";
-    option verbose_name = "vOLT Service Instance";
-
-    optional string description = 1 [max_length = 254, null = True, db_index = False, blank = True];
-}
-
 message OLTDevice (XOSBase){
     option verbose_name = "OLT Device";
     option description="Represents a physical OLT device";
@@ -83,4 +75,13 @@
     optional string admin_state = 6 [help_text = "admin_state", null = True, db_index = False, blank = False, feedback_state = True];
     optional string oper_status = 7 [help_text = "oper_status", null = True, db_index = False, blank = False, feedback_state = True];
     optional string connect_status = 8 [help_text = "connect_status", null = True, db_index = False, blank = False, feedback_state = True];
+}
+
+message VOLTServiceInstance (ServiceInstance){
+    option kind = "vOLT";
+    option owner_class_name = "VOLTService";
+    option verbose_name = "vOLT Service Instance";
+
+    optional string description = 1 [max_length = 254, null = True, db_index = False, blank = True];
+    optional manytoone onu_device->ONUDevice:volt_service_instances = 1 [db_index = True, null = True, blank = False];
 }
\ No newline at end of file