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.
Note: Only organizations that use GitHub Enterprise Cloud can restrict the ability to invite outside collaborators to organization owners. For more information about how you can try GitHub Enterprise Cloud for free, see "Setting up a trial of GitHub Enterprise Cloud."
If your organization is owned by an enterprise account, 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 or internal repository will use one of your paid licenses. For more information, see "About per-user pricing."
In the top right corner of GitHub.com, click your profile photo, then click Your organizations.
Next to the organization, click Settings.
In the "Access" section of the sidebar, click Member privileges.
Under "Repository outside collaborators", deselect Allow repository administrators to invite outside collaborators to repositories for this organization.