A federal judge's order on Tuesday clears the way for the US Internal Revenue Service to demand that UBS (NYSE: UBS - News) provide information about US clients who may be using the Swiss bank's accounts to evade income taxes.

But it also signals a much wider clampdown on offshore tax evasion. Doug Shulman, IRS commissioner, says: "People with hidden foreign accounts can no longer rest easy".

Lawyers and other experts say that US authorities are taking advantage of the momentum provided by the UBS probe to increase overall enforcement of US tax compliance.

Ian Comisky, a partner who specialises in tax litigation at Blank Rome LLP, says: "The government is being aggressive and taking a much tougher stance in general on the stashing of money offshore".

Indeed, the request for a so-called John Doe summons to be served on a foreign bank is unprecedented, according to the US Department of Justice.

The IRS uses such a summons to obtain information about possible tax fraud by people whose identities are unknown.

The summons directs UBS to produce records identifying US taxpayers who held undeclared accounts between 2002 and 2007 with the bank and chose to have them hidden from the IRS.

UBS says it "looks forward to working with the IRS to address the summons".

It adds: "UBS takes this matter very seriously and is working diligently with both Swiss and US government authorities, consistent with Swiss law and the legal frameworks for intergovernmental co-operation and assistance."

Insiders say UBS is eager to reach a settlement with the DoJ as quickly as possible - although this may still take some months.

The bank is now hoping that providing US authorities with the names of some US clients with offshore accounts - without infringing Swiss bank secrecy laws - will satisfy the DoJ and the IRS.

Daniel Richman, professor of law at Columbia University, says: "This is a collision that has been long in coming. It's been clear that, given the interest in federal enforcement authorities in international money flows . . . the agencies would be challenging long-standing foreign secrecy regimes."

The potential number of names that could be revealed would frighten most Swiss bankers, with UBS insiders confirming the group has about 20,000 US offshore clients with about $20bn in assets.

But they also note that some clients will have declared their assets to the US authorities in spite of benefiting from legal provisions not obliging them to do so.

In recent weeks, lawyers say they have received an unusually high volume of calls from worried US clients regarding the filing of the so-called Report of Foreign Bank and Financial Accounts, due this week.

Charles Grice, managing director of CRI Compliance, a regulatory consulting firm, says large amounts of money could "return onshore immediately as no taxpayer can risk looking like they are hiding once the records are out", adding: "The offshore banking system has experienced its biggest earthquake ever."

Indeed, UBS appears to be one part of a bigger project. Mr Shulman says: "The John Doe process is part of the overall IRS effort to stop offshore tax evasion. People should take notice that the secrecy surrounding these accounts is rapidly fading".