Both the Federal Reserve and the Federal Deposit Insurance Corporation (FDIC) said the "living will" plans were "not credible" for Bank of America, Bank of New York Mellon, JPMorgan Chase, State Street and Wells Fargo.
The plans, required in the wake of the 2008 financial crisis, are supposed to demonstrate how the failure of a "systemically important" bank would not devastate the broader financial system.
"The goal to end too big to fail and protect the American taxpayer by ending bailouts remains just that: only a goal," said Thomas Hoenig, vice chairman of the FDIC, in a statement.
Democratic presidential hopeful Bernie Sanders backs the break-up of big banks, while Neel Kashkari, president of the Minneapolis Federal Reserve, has said the financial behemoths "continue to pose a serious, ongoing risk to our nation's economy."
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But Richard Bove, an analyst at Rafferty Capital Markets and a defender of big banks, said the tendency of regulators to stiffen requirements was an overreach that weakens the ability of US banks to compete with other global banks.
Also worrying, the banks have gotten bigger and more complex since 2008 and have "excessively high leverage," Hoenig said.
If one of the banking giants were to fail, the others "would become suspect in their ability to withstand the shock," Hoenig said. "Too easily one failure could become a systemic crisis."
Failure to submit acceptable living wills by the five banks' October 1 deadline could result in higher capital requirements and other toughened standards, such as restrictions on bank operations.