By STEPHEN FIDLER

LONDON -- Swiss private bankers are becoming wary about traveling abroad, underscoring how hard a global crackdown on tax avoidance is hitting the discreet business of providing banking services to the wealthy.

UBS AG, the world's largest manager of private wealth by assets, has barred "client-facing" staff in its wealth-management divisions from traveling abroad -- a move aimed at avoiding further trouble for the bank, which has had two bankers arrested as part of a continuing U.S. investigation into tax fraud.

At the same time, other private bankers in Switzerland are being advised to exercise personal discretion in their travel decisions, people familiar with the matter said.

The travel jitters come as leaders of the Group of 20 developed and developing nations have redoubled efforts to crack open the secretive tax havens where private bankers often park their clients' money. Following last week's G-20 meeting, the Organization for Economic Cooperation and Development included Switzerland on a "gray list" of countries that hadn't yet followed through on promises to comply with its directives on sharing tax information.

Meanwhile, U.S. authorities have been offering leniency to tax evaders in exchange for information on the bankers who helped them hide the money.

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UBS, facing a tax-fraud probe in the U.S., has barred some staff in wealth-management divisions from traveling abroad. Here, a Zurich branch.

For UBS, the travel ban could hinder the lucrative wealth-management business on which it has relied to survive the financial crisis. That business was already declining as U.S. tax authorities pushed the bank to provide them with names of U.S. clients suspected of tax evasion.

UBS has turned over information on nearly 300 accounts as part of a deal in which it admitted to conspiracy to defraud the U.S. Internal Revenue Service. The bank is still under pressure from the IRS to provide information on 52,000 other accounts. UBS says bank secrecy laws forbid it to do so.

Two UBS bankers have been arrested and a further senior executive is being sought in connection with the case. U.S. investigations continue into some of the bank's U.S. clients.

Private clients at UBS withdrew a net 123 billion Swiss francs ($108.17 billion) in 2008, compared with a net inflow of 156 billion francs in 2007. That means the bank lost market share to its chief rival, Credit Suisse Group AG, whose private-banking business saw 51 billion francs of inflows last year. UBS had a total of 1.6 trillion francs under management at the end of last year, compared to 789 billion francs at Credit Suisse.

A UBS spokesman said the travel ban, which went into effect April 1, was a "precautionary measure" that would last at least several more weeks while the bank reviews its compliance procedures.

The ban affects about 1,000 of the bank's roughly 14,000 client advisers.

Most advisers deal only with domestic clients. They can still use the phone and email to communicate with clients in other countries, and clients can visit their advisers.

UBS instructed its private bankers not to travel to the U.S. last year, after U.S. authorities detained one banker in Florida. In February, Swiss authorities banned UBS from engaging in cross-border business with U.S. clients.

Other Swiss banks, including Credit Suisse, said they hadn't introduced blanket travel bans. A spokesman for Zurich-based Julius Baer Holding Ltd. said travel was left to individual bankers' discretion.

In a separate development, the OECD announced that the four jurisdictions it had included in a "black list" of uncooperative tax havens -- Uruguay, Costa Rica, the Philippines and Malaysia -- had agreed to come into line.

Write to Stephen Fidler at [email protected]