First appeal filed against UBS data transfer to US

ZURICH, Nov 21 (Reuters) - A U.S. client of UBS has appealed against Berne's plans to pass Swiss-based bank account data to U.S. authorities as part of a tax fraud probe that could weaken bank privacy, a Swiss court spokesman said on Friday.

UBS, the world's largest bank to the rich, is the target of a high-profile U.S. probe into whether the Swiss bank helped rich Americans evade taxes.

Two Swiss lawyers said earlier this week their U.S. clients had been told by Swiss tax authorities that their UBS bank data in Switzerland would be handed over to the United States. The clients were preparing to fight the decision, the lawyers said.

The appeal, the first related to this investigation, is expected to be followed by dozens of U.S. holders of Swiss bank accounts who are fighting for their financial data to remain confidential, Swiss lawyers have told Reuters.

"An appeal has been filed," a spokesman at the Swiss Federal Administrative Court told Reuters on Friday, confirming a report in Swiss newspaper Le Temps.

"I do not know if there will be more of these, but this is likely."

Swiss lawyers defending U.S. clients say a decision by the court to allow the transfer of some UBS bank data held in Switzerland would make it easier in future to lift the curtain on Swiss bank accounts.

There is no formal deadline for a decision by the Swiss court, and lawyers say the process could take months.

The U.S. tax fraud probe adds pressure on UBS, which is struggling to rebuild its name after making more writedowns than any other bank in Europe in the credit crisis.

UBS shares plunged to an all-time low on Thursday.

Switzerland has a narrower definition of tax fraud than the United States and will only exchange account data with foreign authorities if they can prove tax fraud.

U.S. authorities have requested broad access to thousands of accounts at UBS held by U.S. clients as part of their investigation. Last week they charged the UBS wealth management chief with conspiring to help U.S. clients hide $20 billion from the taxman. (Reporting by Oliver Hirt and Lisa Jucca, editing by Will Waterman)