Bank of America was quoted as saying late on Friday that it was joining other financial institutions in declining to process payments to WikiLeaks, which has angered U.S. authorities with the mass release of U.S. diplomatic cables.
"Bank of America joins in the actions previously announced by MasterCard, PayPal, Visa Europe and others and will not process transactions of any type that we have reason to believe are intended for WikiLeaks," the bank said in a statement, quoted by McClatchy Newspapers.
No one at Bank of America was immediately available to comment.
WikiLeaks has said it will release documents early next year that will point to "unethical practices" at a major U.S. bank, widely thought to be Bank of America.
Several companies have ended services to WikiLeaks after the website teamed up with major newspapers to publish thousands of secret U.S. diplomatic cables that have caused tension between Washington and some of its allies.
"This decision is based upon our reasonable belief that WikiLeaks may be engaged in activities that are, among other things, inconsistent with our internal policies for processing payments," the Bank of America statement added.
WikiLeaks later issued a message on Twitter urging its supporters to leave the bank.
"We ask that all people who love freedom close out their accounts at Bank of America," it said on the social networking medium.
"Does your business do business with Bank of America? Our advice is to place your funds somewhere safer," WikiLeaks said in a subsequent tweet.
In a backlash against organisations that have cut off WikiLeaks, cyber activists have been targeting companies seen as foes of the website.
WikiLeaks founder Julian Assange said on Friday that he was the target of an aggressive U.S. investigation and feared extradition to the United States was "increasingly likely".
U.S. Attorney General Eric Holder has said his government was considering using the U.S. Espionage Act, under which it is illegal to obtain national defense information for the purpose of harming the United States, as well as other laws to prosecute the release of sensitive government information by WikiLeaks.