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 profile.

 - On the left side of your profile page, under "Organizations", click the icon for your organization.

 - Under your organization name, 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.