Jean-Philippe Walter, deputy federal data protection and information commissioner, told Radio Télévision Suisse that he was troubled by the latest transfer of information.
“When we learned that new transfers were made by certain Swiss banks to the United States — transfers of names of their employees — we were astonished,” Walter told the French-language broadcaster on Monday.
“Following the first transfer of information there was an enormous amount of criticism,” he said.
“Questions about the legality of these transfers were posed and in the meantime different legal procedures have been launched with various courts in Switzerland.”
At least two test cases, involving five complainants, have been launched against banks to clarify exactly what personal data was sent to the US.
Both the banks and the federal government are seen as potentially liable in the cases, according to lawyers handling the lawsuits.
Credit Suisse is among the banks that have agreed to cooperate with US authorities fighting tax evasion by releasing files, including correspondence between bank employees and US clients.
The bank’s expat American CEO Brady Dougan earlier downplayed the impact of such exchanges of information.
“Any employee who has followed the rules does not need to worry,” Dougan told Le Temps newspaper.
But Walter urged banks to show “restraint” and to await the result of the current legal cases before transmitting any further such data to the US.
He conceded that he did not have the power to intervene other than to ask banks to stop transferring employee information, although that would not prevent them from doing so.
“The civil justice system has the means to shed light (on the issue) more clearly than we can,” Walter said.
“They should be able to rule on the legality of the transfers of data already made.”
The US continues to track down Americans suspected of evading taxes through the use of Swiss banks after a former UBS banker blew the whistle on the country’s biggest financial institution.
UBS paid the American government 780 million dollars in 2009 after admitting to its involvement in helping US clients evade taxes.
It also passed on to the US the names of thousands of American account holders in what was seen as a breach of Swiss banking secrecy laws, although the deal was approved by parliament.
Since then Washington has stepped up pressure on Switzerland’s banks, forcing Bern to consider making a global settlement with the US to resolve the issue.