The round of new charges stems from a rule, which takes effect on Saturday, that limits the fees that banks can levy on merchants every time a consumer uses a debit card to make a purchase. The rule, known as the Durbin amendment, after its sponsor Senator Richard J. Durbin, is a crucial part of the Dodd-Frank financial overhaul law.

Until now, the fees have been 44 cents a transaction, on average. The Federal Reserve in June agreed to cut the fees to a maximum of about 24 cents. While the fee amounts to pennies per swipe, it rapidly adds up across millions of transactions. The new limit is expected to cost the banks about $6.6 billion in revenue a year, beginning in 2012, according to Javelin Strategy and Research. That comes on top of another loss, of $5.6 billion, from new rules restricting overdraft fees, which went into effect in July 2010.

And even though retailer groups had argued that lower fees were important to keep prices in check, consumers were not likely to see substantial savings. In fact, they are simply going to end up paying from a different pot of money.