Retailers have long fumed about the cost of taking plastic. Unlike with checks, banks charge them fees, known as interchange, to process debit and credit card payments. Debit fees average 44 cents per transaction or about $16 billion a year. The amounts are set by Visa and MasterCard, which own the payment networks and pass the money to the banks.
How Wal-Mart Swiped JPMorgan in $16 Billion Debit-Card Lobbying Battle – Bloomberg