For years, the country’s biggest banks lobbied against a post-2008 financial crisis rule that was intended to shore up their stability and ensure they could withstand steep losses in times of turmoil.

This week, financial regulators led by the Federal Reserve agreed to ease the rule, embarking on what is expected to be an extensive push to loosen the regulatory reins on Wall Street.

The rule in question, the supplementary leverage ratio, mandates that lenders maintain a buffer of easy-to-access money against their total leverage. That measure includes assets such as loans and Treasuries as well as exposures that do not appear on a bank’s balance sheet but generate income, like derivatives.

It is not the first time that the Fed has given the banks a big break on this front. As financial markets melted down at the onset of the Covid-19 pandemic, the Fed offered a temporary reprieve so that banks had more leeway to lend to businesses while staying active in the all-important U.S. government bond market at a time when the economy was reeling from a big shock.

But in loosening the rule in a permanent way, which the Fed voted 5 to 2 in favor of doing on Wednesday, opponents warn that it risks making the financial system more fragile at a time when President Trump’s policies are stoking extreme volatility.

“You lower capital requirements, you build up leverage in this system, which by definition, is going to create less resilience,” said Sheila Bair, who served as chair of the Federal Deposit Insurance Corporation between 2006 and 2011. “You should have a really good reason to do it, and I don’t see the reason.”