Bradley Birkenfeld, who worked in the firm's private banking division, scheduled a "change of plea" hearing for 9 June in federal court in Fort Lauderdale, Florida, according to court papers. The filing notes that the judge "will ask for a full confession."

Mr Birkenfeld, who worked at UBS from 2001 to 2006, had pleaded not guilty earlier this month after he was indicted with Mario Staggl of Liechtenstein. Mr Staggl is a fugitive, prosecutors have said.

The case is part of a growing US investigation into whether the Swiss bank helped clients avoid paying taxes. The probe has added to the trouble swirling around the bank, which has also been hit hard by the subprime loan crisis.

By changing his plea, Mr Birkenfeld is signalling he will help prosecutors and identify other UBS customers who shielded assets to escape paying income taxes, Eileen O'Connor, former head of the Justice Department's tax division, was quoted by Bloomberg as saying.

The indictment alleges Mr Birkenfeld and Mr Staggl attempted to sidestep rules in a U.S.-Switzerland tax treaty that requires information to be exchanged on some financial transactions. The pair - and others not identified by prosecutors - allegedly travelled to the US to pitch their schemes.