A general contractor is demanding that I issue an Unconditional Release for payment that has been mailed but not received or deposited by us. They sent copies of the check as proof that payment is coming. The checks are joint checks if that matters. The GC is now threatening to do a stop payment to our sub-contractor on a different job to force us to issue the UP prior to payment receipt. Is this legal? If I issue the UP and the check bounces can we still get payment from our subcontactor?