The requirements were mandated by Congress after the financial crisis. They are part of new regulations that are intended to prevent another collapse severe enough to require taxpayer-funded bailouts and threaten the broader financial system.
The proposal requires banks with more than $250 billion in assets to hold enough cash and securities to pay out depositors for 30 days during a time of market stress. Banks with more than $50 billion and less than $250 billion in assets would have to hold sufficient amounts to cover 21 days.
"Liquidity is essential to a bank's viability and central to the smooth functioning of the financial system," Fed Chairman Ben Bernanke said before the vote. He said the new regime "would foster a more resilient and safer financial system in conjunction with other reforms."
Hundreds of U.S. banks received federal bailouts during the crisis. Among them were the largest financial firms, including JPMorgan Chase, Goldman Sachs, Citigroup, Bank of America and Wells Fargo. The banking industry has been recovering steadily since then, with overall profits rising and banks starting to lend more freely.