Internal candidates logging into the External career site

Summary:

Has anyone stopped their Internal candidates i.e. those who currently work in your company, from creating a user account on the External career site and applying for a job?

Content (required):

We have stopped External candidates from logging into our Internal career site, but we are unable to stop Internal candidates from creating profiles and submissions on our External career site. This obviously causes issues during onboarding and integration. I can't see anything in the External career site configuration.

Version (include the version you are using, if applicable):

21C.1

Code Snippet (add any code snippets that support your topic, if applicable):