WASHINGTON — A little-noticed provision tucked into regulatory reform legislation by the Treasury Department is causing a furor among large institutions, which say it would effectively ban all derivative transactions between banks and their affiliates.

While the Obama administration argues the provision would make the system safer, bankers say it would do the exact opposite by preventing them from using a risk-reduction tactic blessed by regulators.

"The dual purpose of the overall legislation is to address the causes and consequences of the financial crisis and to reduce systemic risk in the future - yet this provision fails both tests," said Michael M. Wiseman, the head of Sullivan & Cromwell's financial institutions group. "This had nothing to do with the crisis and enactment of this provision would, in fact, diminish the ability of affiliated companies to manage risk on a consolidated basis and, at the same time, could exacerbate interconnectivity among unaffiliated financial institutions."

At issue is a provision that would cover derivatives under Section 23A of the Federal Reserve Act, which restricts a bank's transactions with any single affiliate to 10% of the bank's capital and aggregate transactions with affiliates to 20% of the bank's capital stock and surplus. Under the statute, banks have to fully secure any credit exposure to an affiliate.

Under current law, most derivatives are not treated as a credit exposure, and thus not subject to the statute, but the Treasury successfully included a provision changing that in the House regulatory reform bill passed in December. A draft bill from Senate Banking Committee Chairman Chris Dodd introduced late last year also included the provision, and industry sources expect it to be part of a revised version due out soon.

But industry lobbyists accuse the administration of pretending the provision was little more than a technical change, and most lawmakers are unaware it is even part of the reform bill.

"The provision was put in there by the Treasury and passed in the House bill and it sort of was a sleeper, because it was represented as technical housekeeping amendments," said a former regulator who spoke on condition of anonymity. "In fact it's not. It's much more radical. It really kind of took the industry by surprise. By the time they finally noticed, it had already passed in the House bill before they even realized it was there and figured out what the impact would be on their business, so now it's at a pretty critical juncture."

Bank lawyers, analysts and former regulators said the provision could drastically affect their business. They said that since banks routinely make back-to-back derivatives trades with affiliates throughout the day as a hedging tool, the current business model would easily surpass the 23A caps and effectively prohibit trading with affiliates. As a result, banks will have to offset risk with third parties, they said.

"It's enormous. It's one of the biggest issues in reg reform," said an industry lobbyist who spoke on condition of anonymity. "It will totally change banks' ability to manage risk."

Currently, banks enter into transactions with multiple affiliates but conduct back-to-back trades to put the risk into one place so the holding company can centrally manage it.

"If you can't do back-to-back transactions because you are limited in your exposure … it creates basis risk," the lobbyist said. "It makes it harder to hedge risk and it's a massive systemic problem."

The Obama administration, however, argues the provision would make the system safer and is long overdue. It said the provision will ensure FDIC-insured banks are not overexposed to derivatives transactions with affiliates.

"The fundamental reason why we proposed this reform is to protect FDIC-insured depository institutions in their transactions with affiliates and to prevent the spread of the subsidy inherent in the bank safety net to affiliates," said an administration official who could not be named. "23A today covers loans and guarantees banks provide to affiliates but does not cover derivatives. Credit exposure is credit exposure, regardless of form. If a transaction generates credit exposure of a bank to an affiliate, it should be covered. We've got to close the derivative loophole in the 23A framework."

Karen Shaw Petrou, the managing director of Federal Financial Analytics, said that the Treasury provision makes sense from a policy perspective since it would address credit exposures that are not currently covered.

"What Treasury did was rightly recognize that credit risk now comes in many other ways," she said. "That is a business model changer, and one of the reasons credit risk comes in many other ways is that those ways invaded the old controls designed to curb particularly concentration risk. … The real effort here is to deal with real risk."