The move follows a former UBS banker's guilty plea to conspiring to defraud the Internal Revenue Service (IRS) by assisting US clients to avoid reporting on income in Swiss bank accounts.

Justice officials said the summons, if approved, will compel the UBS to reveal the identities of US clients under "undeclared" accounts, totalling some $20bn.

Last month the former banker, Bradley Birkenfeld, said in a court document that UBS staff assisted wealthy US clients create sham entities and then file false claims to conceal their offshore assets.

US taxpayers are legally required to report all offshore accounts exceeding a total of $10,000 each year.

Doug Shulman, the IRS commissioner, said the information gathered will help detect wealthy tax evaders as well as provide details about how advisors facilitate such abuse.

Rohini Pragasam, a UBS spokeswoman, said in a statement the bank took the matter "very seriously" and was "working diligently" with authorities in both countries.

John DiCicco, the deputy assistant attorney-general of the department's tax division said they were "prepared to seek enforcement" if the Swiss government and bank fails to cooperate on the matter.