The US Department of Justice filed a lawsuit in Miami Thursday asking a federal judge to force Swiss-banking giant UBS AG to disclose to the Internal Revenue Service the identities of the bank's US customers with secret Swiss accounts.

The government alleges that as many as 52,000 US customers hid their UBS accounts from the IRS. Roughly 20,000 of those accounts contained securities, while another 32,000 contained cash, prosecutors said.