ZURICH -- Three Swiss banks have agreed to participate in a U.S. disclosure program aimed at lenders suspected of aiding tax evasion by Americans. The institutions are the first to publicly commit to a trans-Atlantic measure that has stirred controversy.

Valiant Bank, Berner Kantonalbank and Vontobel said they would take part in the joint program between the U.S. Justice Department and Swiss officials, which is intended to have the firms identify any undeclared U.S. assets on their books and pay related fines. Swiss regulators have publicly signaled to banks that it may be better to pay penalties now than risk separate action by the Justice Department.

Banks that participate will disclose the amount of business they generate from U.S. clients and potentially pay fines on undeclared balances held by American customers.The program is part of a U.S. crackdown on tax evasion that has accelerated since the financial crisis began five years ago.

Swiss banks had until Monday to tell the Swiss Financial Market Supervisory Authority, the country's banking regulator, if they would participate. The first deadline for the banks to notify U.S. authorities of their intentions falls at the end of the month.

The program is a key element in a U.S. effort to sidestep Switzerland's bank-secrecy laws. Banks won't disclose customers' names, but the U.S. will obtain other data it could potentially use to identify clients.

The program has met resistance from Switzerland's financial sector, which has complained of the cost of complying, particularly for the country's hundreds of small and medium-size banks.

Concerns have also been raised about the program's lack of specific guidance and whether information given to U.S. officials could implicate Swiss bankers or advisers who may have been unaware they could be violating U.S. laws.

The program allows banks to register in categories based on the level of undeclared U.S. assets on their books. About a dozen banks already under investigation by the Justice Department make up category 1 and aren't included in the voluntary disclosure program. These include Credit Suisse Group AG, Julius Baer Group AG and the Swiss branch of HSBC Holdings PLC. All three banks have said they are cooperating with the probes.

Valiant, a medium-size retail lender in central Switzerland, and Berner Kantonalbank, among the larger of Switzerland's state-backed banks, said they would take part in category 2, which involves a scale of fines based on the amount of undeclared U.S. assets and when they were deposited. Banks applying under category 2 may be on the hook for fines, but may also receive nonprosecution agreements. They will have 120 days to make their disclosures from the time they tell the U.S. they plan to participate in the program but may be eligible for a single 60-day extension.

Valiant said less than 0.1% of its 400,000 clients are American, while Berner Kantonalbank said less than 0.2% of client assets come from people "domiciled" in the U.S.

Vontobel, a private-banking and asset-management specialist, said it would participate as a category 3 institution, one that declares it hasn't helped Americans evade taxes. Vontobel said it had "future-proofed" its U.S. business by registering a unit for those clients with the U.S. Securities and Exchange Commission.

Category 3 banks don't have to provide information to the Justice Department until July but could face repercussions if it is determined they should have filed some six months earlier as category 2 institutions.

Banks admitted to category 3 could receive a "nontarget letter" from the regulator, a legal confirmation that a lender isn't under investigation.

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