It seems like there used to be a way to do this, but allow a setting that prevents users (even ones from the same domain) from inviting new users (also from the same domain, but also any domain) as a way to manage subscriptions and cost.
Hey Jennifer,
If I am understanding correctly it is possible to restrict users from inviting new users (with the same domain or not) under the Admin settings > Security > Login.
You will need to ensure that the outlined option is not selected.
Let me know if this helps 
Hi Bianca,
Yes, this is what I was looking for. Thank you for directing me here, I appreciate it!!
- Jen