To critics, the changes to banking regulations that lawmakers slipped into a spending bill is nothing more than a giveaway to banks. And the losers will be taxpayers, who'll be on the hook for future bailouts.

But to Wall Street, the change is a common-sense revision to a regulation that went too far in the first place.

To hear bankers and their lobbyists say it, the regulation that Congress is poised to wipe away would make the banking system more risky -- not less risky.

At the center of the dispute are arcane financial instruments known as loan swaps. Those are contracts between banks used to spread the risk in their loans and trades.

A rule that would have limited the use of those swaps by commercial banks (think Citigroup (C) or JPMorgan Chase (JPM)) was essentially stripped out of the law during budget negotiations in recent days.

The move sparked outrage, mostly from progressives but also from some conservatives.

"This provision is all about goosing the profits of the big banks," said Democratic Senator Elizabeth Warren. The change in the law "will simply confirm the view of the American people that the system is rigged."

Swaps were ground zero of the 2008 meltdown of the global financial system. That's because banks had bundled risky mortgage loans and sold them as bonds. And to make the bonds more appetizing to investors, swaps were created as a form of insurance that the bonds would pay as promised.

So when the housing bubble burst and so many people couldn't afford their mortgage payments anymore, those bonds blew up. And the banks and firms like AIG (AIG) that held the suddenly-toxic swaps contracts needed bailouts.

Related: Congress right back where it started

Fast forward to 2009 and 2010,when Congress passed the Dodd-Frank financial reform act. The idea was to prevent a repeat of the 2008 meltdown.

One provision of Dodd-Frank to protect taxpayers was a rule saying major banks couldn't use their normal commercial banking operation to create, buy or trade these kinds of swap contracts. Instead those contracts had to be held by separate entities whose assets were not insured by the Federal Reserve or the Federal Deposit Insurance Corp.

"If Wall Street banks want to gamble, Congress should force them to pay for their losses, and not put the taxpayers on the hook for another bailout," said a letter signed this week by both one of the most conservative senators, David Vitter, and one of the most liberal, Sherrod Brown.

Even though Dodd-Frank was signed into law more than four years ago, the rules to limit banks gambling with taxpayer-backed money are not yet completely in place. That opened the door for a $6 billion dollar loss by JPMorgan Chase (JPM) due to actions of a trader known as the "London Whale."

But as part of a bill to avert a government shutdown, Congress voted to roll back the rule -- a victory for the banking industry. Banks insists they use swaps in order to limit their risks, not make them more risky. Without swaps, it will be the Main Street customers, not Wall Street, who will be hurt, they argued.

"Hedging and mitigating risk are not only good business practices, but are important tools that banks use to help borrowing customers hedge their own business risks," said the statement James Ballentine, the head of congressional relations for the American Bankers Association.