'Checkout fee' for using a credit card.

http://money.cnn.com/2013/01/27/pf/checkout-fee/index.html?iid=s_mpm

Visa, MasterCard and nine major banks agreed to a $7.25 billion deal to settle a 'checkout fee' for customers when they buy something with plastic. As part of the settlement credit card issuers would reduce these "swipe fees" - fees paid by merchants to issuers when cards are used - but only for eight months.This fee doesn't apply yo purchases made using debit cards though. 
Many stores from the nation's largest retailer down to small businesses have lamented the agreement. Walmart said it would cost consumers "tens of billions of dollars each year", while Target called the agreement "bad for both retailers and consumers."