An outside collaborator is a person who is not a member of your organization, but has access to one or more of your organization's repositories. For more information, see "Adding outside collaborators to repositories in your organization."
By default, anyone with admin access to a repository can invite outside collaborators to work on the repository. You can choose to restrict the ability to add outside collaborators to organization owners only.
You may not be able to configure this setting for your organization, if an enterprise owner has set a policy at the enterprise level. For more information, see "Enforcing repository management policies in your enterprise."
Adding an outside collaborator to a private repository will use one of your paid licenses. For more information, see "About billing for your enterprise."
In the top right corner of GitHub Enterprise Server, click your profile photo, then click Your organizations.
Next to the organization, click Settings.
In the left sidebar, click Member privileges.
Under "Repository outside collaborators", deselect Allow repository administrators to invite outside collaborators to repositories for this organization.