In papers filed in federal court in Miami, the Justice Department acknowledges that in seeking to obtain the account information from UBS AG (NYSE:UBS) of Zurich, Switzerland, the Internal Revenue Service isn't looking for specific individuals suspected of harboring assets in the bank. Instead, it wants the IRS to be allowed to serve what is called a "John Doe" summons on the bank to obtain information about possible tax fraud by people whose identities are unknown.

The Justice Department action follows the June 19 guilty plea by former UBS banker Bradley Birkenfeld, who claims the Swiss bank had about $20 billion of assets under management in "undeclared" accounts for U.S. taxpayers.

Birkenfeld pleaded guilty to conspiring to defraud the IRS by assisting UBS clients in avoiding U.S. reporting requirements on income in Swiss bank accounts.