I'd call a lawyer. I'd try to get the ACLU involved (they can sometimes be good for something--and since it's a "free speech" rather than a RKBA issue they might actually take on the issue). Even if there is a provision in the lease it may not be legal. Per the lawyer I hired when I had a lease dispute, there are certain rights that one cannot sign away and any document purporting to do that is null and void.