Avis - Removing the rear seats

I have a Tahoe and would like to temporarily remove the 3rd row of seats to haul some stuff. However, they won't pull out of their mechanism, following the steps on the seat back. I've dug around and cannot see if Avis put a locking mechanism (bolt, etc) there to prevent their removal. Does anyone have any suggestions?

I know this isn't really Avis related, but it's an Avis car, they have lots of them in their fleet and Google isn't much help, so I thought someone here might have some clues.

Thanks!