Swiss bank UBS AG has forbidden its travel client managers from traveling abroad.

Swiss bank UBS AG, which is being investigated by the U.S. for tax fraud, said Sunday that it has forbidden its travel client managers from traveling abroad.UBS managers who handle clients from countries other than Switzerland are barred from going overseas, spokeswoman Eveline Mueller said.Mueller declined to say whether the restriction aimed at protecting UBS managers from U.S. authorities. The travel ban affected the bank's international business with all countries, she said.UBS has been involved in a dispute with the United States over wealthy Americans who have assets in Switzerland's biggest bank. It is assessing the guidelines and rules of behavior related to its international asset management business, Mueller said.The bank has provided U.S. tax authorities with the details of 255 wealthy Americans suspected of tax fraud, but refuses to identify about 50,000 more U.S. account holders Washington wants.Former UBS manager Martin Liechti was held over two months for witness questioning in the U.S. last year in connection with the tax fraud investigation.U.S. authorities in January charged another senior executive with UBS, Raoul Weil, with conspiring to hide $20 billion in assets from the IRS using secret overseas accounts for thousands of wealthy customers. Weil's attorney says that his client is innocent.And a former UBS banker, Bradley Birkenfeld, pleaded guilty last year in Fort Lauderdale to fraud conspiracy charges and has been cooperating extensively with U.S. investigators.Birkenfeld has not yet been sentenced.