Instead, Visa provides an electronic network that acts like a tollbooth, processing the transaction between merchants and banks and collecting a fee that averages 5 or 6 cents every time. For the financial year ended in June, Visa handled 40 billion transactions. Banks that issue Visa cards also pay a separate licensing fee, based on payment volume. MasterCard, which is roughly half the size of Visa, uses a similar model.

Image Mitch Goldstone, in his digital photo-processing shop in Irvine, Calif., is part of a suit against Visa and MasterCard. Credit... Monica Almeida/The New York Times

“It’s a penny here or there,” said Moshe Katri, an analyst who tracks the payments industry for Cowen and Company. “But when you have a billion transactions or more, it adds up.”

With debit transactions forecast to overtake cash purchases by 2012, the model has investors swooning: Visa’s stock traded at $88.14 on Monday, near a 52-week high, while shares of MasterCard, at $256.84 each, have soared by more than 450 percent since the company went public in 2006.

While there is little controversy about the fees that Visa collects, some merchants are infuriated by a separate, larger fee, called interchange, that Visa makes them pay each time a debit or credit card is swiped. The fees, roughly 1 to 3 percent of each purchase, are forwarded to the cardholder’s bank to cover costs and promote the issuance of more Visa cards.

The banks have used interchange fees as a growing profit center and to pay for cardholder perks like rewards programs. Interchange revenue has increased to $45 billion today, from $20 billion in 2002, driven in part by the surge in debit card use.

Some merchants say there should be no interchange fees on debit purchases, because the money comes directly out of a checking account and does not include the risks and losses associated with credit cards. Regardless, merchants say they inevitably pass on that cost to consumers; the National Retail Federation says the interchange fees cost households an average of $427 in 2008.

While the cost per transaction may seem small, at Best Buy, the biggest stand-alone electronics chain, “these skyrocketing fees add up to hundreds of millions of dollars every year,” said Dee O’Malley, director of financial services. “Every additional dollar we are forced to pay credit card companies is another dollar we can’t use to hire employees, or pass along to our customers in the form of savings.”