Need to disable "New User" button from internal career section

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Hi,

We have created a internal career portal for internal employees, but if somehow external person gets the URL of internal career section, he/she can create new user account and start applying for internal jobs. We need to disable or hide that button so that only internal employees those already have account can apply on internal portal. Is it possible to disable or hide that button? or any other workaround to restrict external persons to create account on internal career portal?