Washington, D.C. ? A government lawsuit Thursday seeks the identities of tens of thousands of possible U.S. tax cheats who hid billions of dollars in assets at the Swiss-based bank UBS AG. A defiant Swiss president pledged to maintain his country’s bank secrecy laws.

In the suit filed in Miami, the Obama administration wants UBS to turn over information on as many as 52,000 U.S. customers who concealed their accounts from the U.S. government in violation of tax laws.

“At a time when millions of Americans are losing their jobs, their homes, and their health care, it is appalling that more than 50,000 of the wealthiest among us have actively sought to evade their civil and legal duty to pay taxes,” the acting assistant attorney general, John DiCicco, said in a statement.

A deal announced Wednesday provides access to about 250 to 300 UBS customers who used Swiss bank secrecy laws to hide assets.

To avoid prosecution, UBS agreed to pay $780 million, which Justice Department officials said was the largest ever in a criminal tax case.