There's a school of thought that says that increasing the POS limit could be adverse to the customer. It's a stretch, I think, unless you ever get into a claim that the customer lost money on unauthorized EFTs due partially to the increased limit.
I recommend you notify your customers, but do so in a positive (can you hear the Marketing Stampede) way. There's no advance notice requirement, since this isn't truly a change in terms notice. But you might also consider including information on how a customer might lower the POS or cash limit to reduce risk.
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John S. Burnett
BankersOnline.com
Fighting for Compliance since 1976
Bankers' Threads User #8