Unless you provide for an alteration to the provisions of the UCC in your deposit contract, you could run into a problem. I suggest you discuss your idea with counsel before doing anything.
Suppose that a customer calls and places a stop payment on his check. You tell the customer that you will send a written copy of the order and that he must return it to you. The customer then changes his mind and wants the check paid, so he decides not to sign the written stop order, and assumes that it will "drop off" at the end of two weeks. The check is presented on day 20, and you bounce it for stop payment.
Your customer, IMO, might have a case for wrongful dishonor under the UCC.
Your attorney can tell you how to avoid that risk. Ideas might include updating your deposit contract to provide for effective periods of 6 months (or longer) on oral and/or written stop orders. Perhaps your attorney would tell you to inform the calling customer that the stop order will be effective for six months and that he only needs to contact you to correct information (based on a confirmation you'll send, if that's what you'll do) or to cancel the stop order.
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John S. Burnett
BankersOnline.com
Fighting for Compliance since 1976
Bankers' Threads User #8