In escalating efforts by the US government to combat tax evasion, officials will advance their campaign to force UBS to release the names of thousands of American customers holding offshore accounts with the Swiss bank.

The Department of Justice, in a filing with a Miami district court, said UBS should be ordered “to comply in full’’ with an Internal Revenue Service summons asking for the identity of 52,000 undisclosed accounts.

In February, UBS agreed to pay $780m as part of a settlement of a criminal investigation by the Department of Justice (DoJ) that the bank helped clients evade hundreds of millions of dollars in US taxes. However, UBS is still embroiled in a separate civil action demanding details of the bank’s US offshore clients.

The DoJ was quoted as saying, “UBS must disclose the identity of every US taxpayer with an undisclosed UBS account so that every US customer with an undisclosed account will get right with their government,” and added that “the US has a strong national interest in making sure that all US taxpayers comply with the tax laws, including disclosing their offshore accounts, and paying all the taxes they owe’’.

In its defence, UBS argues that yielding to the US demands would involve breaking Swiss law and such issues are best negotiated by governments, rather than legal actions against companies. Swiss government and important trade federations are endorsing this stance.

 A spokesman for UBS recently confirmed this position stating, “Our position remains that the enforcement of the summons would require UBS to violate Swiss law and is inconsistent with treaty frameworks,’’

While trying to comply with the summons without violating Swiss law the bank still, “continues vigorously to oppose the enforcement of the summons”.

The bank is due to go to trial over the lawsuit in Miami on July 13 and the court case is expected to be long and complex. Meanwhile, the pursuit of undeclared accounts by the US has prompted some individuals to disclose accounts voluntarily.

“Timeliness in making the application from the banks or other sources is still the key point in being ahead of the Internal Revenue Service (IRS) finding out from the banks or other sources that the US person has an account in a foreign country,’’ said David Gannaway, director of litigation and corporate financial advisory services at Marks Paneth & Shron.