For Admins Only
You have to be an organisation owner or admin in order to make these changes.
In your organisation, you can set whether all users or admin's only can invite members.
- Click on the gear at the top left and go to "Manage members"
- Click on "Invite members" at the top right
- Scroll down to the checkbox "Only Admins and I can invite new members" and activate or deactivate as desired.