WASHINGTON — The United States warned Switzerland Tuesday of legal action if it reneges on a deal allowing UBS bank to provide the names of thousands of account holders allegedly dodging American taxes.

The warning came after Swiss parliamentarians rejected an out-of-court settlement among Switzerland, the United States and UBS for the bank to reveal the identities of about 4,450 American clients suspected of tax evasion.

"We continue to monitor the events in Switzerland, and we stand ready to pursue all legal options available to us should the Swiss fail to provide the required information," said Frank Keith, spokesman for the Internal Revenue Service, the US government tax collection and enforcement agency.

"We have an agreement with the Swiss government. We expect that the Swiss government will continue to honor the terms of the agreement," he said.

Meanwhile, a senior US senator called on US authorities Tuesday to seek court action to force UBS to provide the names of the suspected US tax cheats.

Any rejection of the treaty by Switzerland would be an "international embarrassment that can be laid at the feet of Swiss legislators who are willing to continue to allow their banks to facilitate US tax evasion," said Democratic Senator Carl Levin.

"The United States should reject any further attempts by the Swiss to delay the UBS case," said Levin, who heads the investigations panel of the US Senate committee on homeland security and governmental affairs.

"It is time to move forward with the summons in court and force UBS to provide the names and account information for all 52,000 suspected US tax cheats," he said in a statement.

As part of an August 2009 deal the United States agreed to give up its right to all 52,000 names in exchange for getting prompt access to information on key accounts, Levin said.

The Swiss lower house of parliament voted Tuesday against the deal after the Senate approved it last week.

The deal, which had challenged Switzerland's sacrosanct banking secrecy, would now return to the Senate and depending on the upper house's decision, the accord could then be put again for a vote in the lower chamber.

With the summer parliamentary session ending on June 18, lawmakers will have to find a compromise by then.

The Swiss government has repeatedly emphasized the importance of the deal, warning that a failure to approve it would hurt the Swiss financial industry.

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