It's because so many people have left on 'emergency leave' and for vacations that now a lot of employers are no longer issuing exit permits, or if they do they make these requests.
It's probably not legal for them to demand a deposit, but then it's not legally required for them to give you an exit permit either.
If you try to lodge a legal case about it, then you will be on a travel ban until the case is resolved, and then you really can't go on vacation!!