You can prevent members from changing the visibility of organization-owned repositories on your GitHub Enterprise appliance.
When you prevent members from changing repository visibility, only site administrators have the ability to make public repositories private or make private repositories public.
Sign in to your GitHub Enterprise instance at
In the upper-right corner of any page, click .
In the left sidebar, click Admin center.
Under Users can change repository visibility, select the drop-down menu, then click Disabled.