As legal actions continue surrounding ex-UBS clients and staff in allegedly hiding funds, the Internal Revenue Service said Gadola conspired with a Swiss banker to encourage US clients who had not told the IRS about UBS accounts to open them at Basler Kantonalbank.

Gadola, a Swiss citizen, pleaded not guilty.

Gadola and the banker told clients not to join a partial amnesty programme that led 18,000 US citizens to disclose offshore accounts to the IRS, prosecutors said, the news service reported.

The prosecution comes in the wake of last year’s legal battle between UBS and the US authorities over the latter's demand for client account details from UBS. In an agreement last August between the US and Swiss governments, the Zurich-listed bank handed over up to 4,450 account details as part of a civil case; in February, as part of a separate, criminal case, the bank paid a $780 million fine to settle charges that it helped clients evade taxes.

UBS, along with several other Swiss banks, no longer provides offshore banking to US clients.

The case has focused attention on how determined countries such as the US are in stamping out tax evasion. One difficulty has been that under Swiss law – in contrast to the law of countries such as the US and UK – tax evasion is not a crime.

The Bloomberg report said that Gadola and the unidentified banker told US clients “not to disclose their undeclared accounts at Basler Kantonalbank and other banks to the US government, including the IRS,” according to a charge filed in federal court in Florida.