Have you been cheating on your bank? The twin towers of the lending industry sure hope so. In fact, they are alleged to have done everything in their power -- legally or not -- to assure that you use their debit cards when it's your turn to pony up at the checkout counter.

According to recently unsealed depositions and company memos (we just love this secret stuff!), Visa USA, Inc. and MasterCard International, Inc. systematically set out to keep smaller credit networks out of the debit card business. According to a report in today's Wall Street Journal, the card giants spent millions to convince banks to curtail their debit card business with regional issuers. The suit also charges them with forcing retailers to favor Visa and MasterCard's costlier and less efficient debit card offerings.

The federal antitrust suit alleges that the Plastic Powers That Be lorded over the credit card market by threatening retailers with pulling access to credit card sales if they didn't take their debit cards. (Such allegations are nothing new for the companies.) According to the Journal's report, Visa and MasterCard went so far as to dress up their debit cards to deceive merchants into believing they were credit cards.

What's a retailer to do? Fight back, that's what. The class action suit is led by the world's largest merchant -- Wal-Mart(NYSE: WMT) -- but nearly every retailer in the U.S. is a plaintiff. Retailers say they paid billions of dollars in extra processing charges to accommodate Visa and MasterCard's debit cards.

Oh, and guess who ended up paying the padded costs? Yup, you and me.