The US Federal Reserve says it will test 31 major US banks in 2012 to see if they can deal with a severe economic shock, part of Wall Street reforms aimed at preventing a fresh financial crisis.

The announcement on Tuesday means the Fed is adding 12 new banks to its stress-testing regimen after examining 19 in 2011.

It said any bank or bank holding company with assets worth more than $US50 billion ($A50.82 billion) will now be subjected to tests.

“The level of detail and analysis expected in each institution’s capital plan will vary based on the company’s size, complexity, risk profile, and scope of operations,” the Federal Reserve said.

Under the rules, the central bank and regulator could veto bigger dividend payments or stock buy-backs if firms are judged strong enough to withstand a crisis.

The six largest firms “will be required to estimate potential losses stemming from a hypothetical global market shock”, much like that seen in late 2008, the Fed said.

Banks will be asked to present their plans by January 9, 2012 and some of the results will be published.

Meanwhile US retail groups are suing the Federal Reserve, claiming the central bank didn’t follow the law when it set a cap on fees that banks can charge merchants for handling debit card purchases.

The National Retail Federation and other groups charge in the suit that the Fed buckled under pressure from bank lobbyists when it set the cap at an average of about 24 cents per transaction in late June. The cap, which took effect on October 1, was initially proposed at 12 cents.

The merchant groups maintain that in raising the cap, the Fed considered expenses that the law did not allow. The law is part of the financial regulatory reform passed in July 2010.

Banks lobbied hard against the rule, which cut fees that averaged around 44 cents per transaction.