Answer:
Get your attorney involved. Although there is a warranty provision in the UCC that establishes your liability for the forged endorsement, your attorney may be able to argue successfully that the underlying claim for payment (from the contractor) is without merit. If the drawee bank has not yet paid its depositor for the original claim, your counsel may be able to defeat the claim altogether. Your bank shouldn't be responsible for resolving the contractor's dispute with the IRS!
First published on BankersOnline.com 9/13/10