1. Login to Symantec Endpoint Protection Manager
2. Goto Clients Tab
3. Select the Group to which you want to apply the policy
4. On Right Hand Side goto policies tab
5. Goto Location Specific Settings.
6. Click Tasks to and Right Click on "Client User Interface Control Settings"
7. Click Edit Settings.
8. Select Server Control
9. Click Customize.
10. Uncheck Allow users to Enable and Disable Network Threat Protection.
11. Click OK
Mark as a solution if it works