Feb. 23 (Bloomberg) -- UBS AG, Switzerland’s largest bank, must respond by April 30 to a U.S. lawsuit seeking to force disclosure of the names of 52,000 Americans who allegedly used Swiss accounts to hide money from tax authorities, a judge said.

The ruling came in the first hearing since the U.S. sued UBS on Feb. 19, a day after the bank agreed to pay $780 million and disclose some names to defer prosecution on a charge that it conspired to help wealthy Americans evade U.S. taxes.

U.S. District Judge Alan Gold in Miami also ruled that the Justice Department must respond by June 30 to the bank’s April 30 filing. No lawyers were present in the courtroom for the telephonic conference.

The Internal Revenue Service seeks to strike a blow at historic Swiss bank secrecy, which the Justice Department claims has robbed the U.S. Treasury of taxes. Zurich-based UBS said in a court filing on Feb. 20 that the lawsuit is a violation of Swiss sovereignty and seeks to compel bank employees to violate criminal laws by forcing disclosure of names.

The Swiss government has disclosed to the IRS the names of UBS customers who it ruled violated Swiss tax-fraud law. Unlike U.S. authorities, the Swiss don’t consider tax evasion to be a crime.

Gold scheduled the next status conference for May 7.

The case is U.S. v. UBS AG, 09-20423, U.S. District Court, Southern District of Florida (Miami).

To contact the reporters on this story: David Voreacos in Newark, New Jersey, at dvoreacos@bloomberg.net; Mort Lucoff in Miamit .

Last Updated: February 23, 2009 18:57 EST