US ratings agency Standard and Poor's cut its ratings for eight major American banks on Thursday, saying they cannot count on government help again in case of trouble.
"We now consider the likelihood that the US government would provide extraordinary support to its banking system to be 'uncertain' and are removing the uplift based on government support from our ratings," the agency said in a statement.
The eight constitute the group of so-called "systemically important banks", a technical term for "too big to fail".
The longterm ratings for Bank of America, Citigroup, Goldman Sachs and Morgan Stanley were cut by one level to BBB+.
Bank of New York Mellon, State Street and Wells Fargo were also cut a notch, to A, while JP Morgan went down to A-.
The move concerns only the banks' holding entities, not their underlying operational entities, Standard and Poor's said.
In October, the US central bank, the Federal Reserve, urged major banks to bolster reserves to avoid the need for a taxpayer-funded bailout in case of any future insolvency.
If they accept the idea, the banks will have to issue bonds to the tune of $120 billion dollars (114 billion euros) that holders can convert into shares in the event of a bankruptcy.
Major financial institutions in the United States were bailed out by the government during the 2008 financial crisis, but the administration was unlikely to be as supportive again next time round, Standard and Poor's warned.