Organization owners, and members with admin privileges for a repository, can invite outside collaborators to work on the repository. You can also restrict outside collaborator invite permissions to only organization owners.
- 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 invitations", select Allow members to invite outside collaborators to repositories for this organization.

- Click Save.