The United States Internal Revenue Service is calling on the world's biggest accounting firms to strengthen its campaign against tax dodgers, two days after securing the backing of a federal court to track down UBS customers suspected of evading US taxes using Swiss accounts.

The IRS has scheduled a conference call for Tuesday with accountants such as Ernst & Young and PricewaterhouseCoopers to agree ways in which their auditing departments can aid the US Government's quest to clamp down on tax evasion by American citizens.

Barry Shott, a deputy IRS commissioner in charge of international taxes, wrote in an e-mail to the six firms: “We are concerned generally by what we are seeing and hearing about the way some foreign banks are behaving with relation to the payment of US taxes by their customers.”

The IRS declined to comment on the call, which is also thought to include Deloitte & Touche, Grant Thornton, KPMG and BDO Seidman.

Although auditors are not responsible for pursuing suspected cases of tax fraud, the Government wants them to assist in its “Qualified Intermediary” programme, which was set up in 2000 to give foreign banks operating in the US lenient tax treatment in return for revealing customer details.

In 2003, the most recent year for which there are figures, $5 billion in unpaid taxes was clawed back from US citizens.

The IRS was emboldened in its pursuit on Tuesday when a federal judge in Miami took the unprecedented step of demanding that UBS hand over records identifying American taxpayers with accounts in Switzerland.

The US Justice Department believes that as many as 20,000 UBS customers collectively have about $20 billion in assets in “undeclared” accounts and that the bank has helped them to avoid about $300 million in taxes. Doug Shulman, the IRS commissioner, said: “People should take notice that the secrecy surrounding these accounts is rapidly fading.”

UBS said that it would work closely with the IRS but hinted that the release of the names was still not a foregone conclusion because of the need for it to comply with Swiss law, which prohibits banks from disclosing confidential information without client approval.

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