The financial regulation overhaul passed last year created a new agency to protect consumers and promised sweeping changes for everything from Wall Street investment firms to Main Street banks. But a relatively small provision — added as an amendment late in the process — is now at the center of a massive lobbying effort pitting retailers against banks.

This is a multibillion-dollar fight about who should bear the cost when you swipe your debit card to buy a bag of Skittles, a cup of coffee or a television.

Right now, the retailer pays a charge to your bank and either Visa or Mastercard. Hidden to consumers, it’s called an interchange fee. Nationwide, these fees cost retailers about $16 billion a year. But thanks to the financial overhaul legislation, costs to retailers are about to go down.

Banks and card companies Visa and MasterCard are poised to lose billions. So, they’re pushing legislation to delay the start of the new rule.

“Congress is going to decide who’s going to win. Is it a big business or the biggest business?” says Paul Blumenthal, senior writer at the Sunlight Foundation, an open-government group.

He’s watching this fight closely. On one side, you’ve got Wal-Mart, Home Depot, Amazon and the convenience store on the corner. And on the other, you’ve got Visa, MasterCard, Wells Fargo and the credit union down the block.

“Senators and congressman see this as the premier lobbying issue at the moment,” Blumenthal says. “This seems to be the one that sticks out as the one that they’re being lobbied on the most.”

Lobbying Efforts Intensify

There’s a huge amount of money being spent, but it’s hard to get a read on just how much. In the first quarter of this year, the coalitions for the retailers and the banks spent a combined $340,000 on lobbying. But it’s not just the coalitions. Individual retailers, individual banks and all their trade associations are lobbying on this, too.

Then there are the ads — even on the subway in Washington, D.C. One reads: “Washington is helping giant retailers clean out your wallet.”

Trish Wexler, a spokeswoman for the Electronic Payments Coalition, the group of banks and credit unions behind the ads,says they have ads running on about 100 railcars.

“When you talk about it in terms like interchange fees, or merchant discount fee, you know, we kind of tune it out as average Americans,” she says. “My job was to make sure that people understood that this means that our debit card is going to end up costing us more as a result.”

The banks and credit unions say that if the rule goes through and they lose $12 billion a year in interchange fees, they’re going to have to raise fees, slash rewards or stop issuing debit cards altogether. Retailers have said consumers will end up paying the extra costs. Both sides say if the other guys win, consumers lose.

Dueling Business Interests

Both the banks and the retailers say they have the little guys on their side.

“We’ve had over 250,000 of our members contact their representatives in Washington, just in the last month,” says Bill Cheney, president of the Credit Union National Association.

Retailers are calling and writing their members of Congress, too, asking that they let the rule go into effect as planned.

“We already worked on this one, we already figured that this isn’t fair,” says Tariq Hussein, a 7-Eleven franchisee in Washington, D.C. “Why reopen now? What happened?”

What happened is that $12 billion is a lot of money. If Congress doesn’t act, which is entirely possible, then the new rule will take effect July 21. And sometime after that, maybe we’ll learn how consumers came out. Copyright 2011 National Public Radio. To see more, visit http://www.npr.org/.