There’s no question these are tough times for retailers. Consumer spending is weak, and the hangover from the housing collapse could tip the economy into recession. There’s a jolt on the way from rebate checks, but retailers are gazing at a different pot of gold —credit card fees, in particular the interchange fees used between banks in the MasterCard and Visa systems. Unfortunately, their proposed solution, now embodied in federal legislation, would have serious unintended consequences for consumers and could worsen the country’s economic problems.