A Swiss court ruled on Friday that banking watchdog FINMA violated Swiss laws by authorising the transfer of data of 300 UBS clients to US tax authorities.

"The Federal Administrative Tribunal ... ruled that the decision of the FINMA on February 18, 2009 to order the transfer of banking data of UBS clients to authorities of the United States of America violates the law," it said. In a bid to settle charges of tax fraud in the United States, Switzerland's banking flagship UBS agreed in February to pay US authorities $780 million and hand over details of about 300 clients.

But the Swiss court noted that "even if FINMA is in a critical situation due to threats of a penal proceeding against UBS from the US authorities, it is not authorised to allow the transmission of banking data concerning clients outside of the ordinary international administrative assistance procedure."

Only the Swiss government and the Parliament are authorised to allow for banking secrecy rules to be lifted by evoking the law of "constitutional necessity". Banks in Switzerland are not authorised to provide any data on their clients to authorities, unless there is clear evidence of fraud or money laundering.