You can set base permissions that apply to all members of an organization when accessing any of the organization's repositories. Base permissions do not apply to outside collaborators.
If someone with admin permissions to an organization's repository grants a member a higher level of permission for the repository, the higher level of permission overrides the base permission.
- In the top right corner of GitHub, click your profile photo, then click Your organizations.
- Click Settings next to the organization.
- In the left sidebar, click Member privileges.
- Under "Base permissions", use the drop-down to select new base permissions.
- Review the changes. To confirm, click Change default permission to PERMISSION.