Group calls for U.S. to break up Bank of America

However, the petition is a dramatic criticism of regulators who have so far done little to shrink giant banks after the 2007-2009 financial crisis.

"Bank of America currently poses a grave threat to U.S. financial stability by any reasonable definition of that phrase," the 24-page petition said.

It said Bank of America, the nation's second-largest bank, is too large and complex, and that its financial condition could deteriorate rapidly at any moment, potentially causing the market to lose confidence in the bank.

"An ensuing run on the bank could cause a devastating financial crisis," the petition said.

David Arkush, director of Public Citizen's Congress Watch division, said a lot of the group's concerns apply to other large banks, but that Bank of America is the institution most exposed to the housing crisis.

"Regulators need to get ahead of this and act proactively to reform Bank of America," Arkush said.

Bank of America has had a tough time emerging from the financial crisis, particularly because of mortgage losses tied to its 2008 Countrywide Financial purchase.

The bank's stock slid 58 percent last year as investors expressed disappointment with the speed of a turnaround and fear about the bank's ability to comply with new capital rules.

Bank of America has fared better this year. It reported improved capital levels in its fourth-quarter earnings report last week, and its stock has risen 31 percent since the start of the year.