Credit Suisse has started to notify some US clients suspected of offshore tax evasion that it intends to hand their names to the Internal Revenue Service, with the help of Swiss tax authorities, Reuters reports, citing a notification letter it has seen.

The handover of names and account details will take place following a recent formal request for the information by the IRS, the report said.

"The US Internal Revenue Service (IRS) recently submitted a request for administrative assistance to the Swiss Federal Tax Administration (SFTA) pursuant to the 1996 double tax treaty between Switzerland and the US, seeking information with regard to accounts of domiciliary companies belonging to certain US persons as beneficial owners (the Treaty Request). In connection with the IRS Treaty Request, the SFTA has issued an order directing Credit Suisse AG to submit responsive account information to the SFTA," Credit Suisse said in an emailed statement to this publication.

US authorities suspect that tens of thousands of US citizens have been stashing money in secret Swiss bank accounts. Already, the US and Swiss governments have forced UBS, Switzerland’s biggest bank, to hand over client account details in a civil and criminal case concluded in 2009.

The letter, on a Credit Suisse letterhead, is dated 2 November and was sent from the bank's Zurich headquarters and is signed by two senior Credit Suisse executives. It cites a formal request made by the IRS to the Swiss Federal Tax Administration, or SFTA, via a tax treaty between the two countries, the report said.

"The IRS is seeking information with regard to accounts of certain US persons owned through a domiciliary company (as beneficial owners) that have been maintained with Credit Suisse," the letter said.

"In connection with the IRS treaty request, the SFTA has issued an order directing Credit Suisse to submit responsive account information to the SFTA," the letter said. "This order is immediately executable and Credit Suisse as an information holder has no right to appeal,” the letter said.

The IRS request reportedly covers accounts maintained at any time over the period from 1 January 2002 through 31 December 2010. The letter was signed by Michel Ruffieux and Stephan Gussman, both managing directors at Credit Suisse.

So far, no information with regards to how many clients are involved in the data transfer has been announced. Analysts at Vontobel, the Swiss private bank, said the issue on a possible tax transfer by Credit Suisse to the US authorities is “advancing faster than expected, which we believe is positive for Credit Suisse as we could potentially see a conclusion to this matter earlier than we previously expected”.

Vontobel confirmed its “hold” stance on Credit Suisse’s stock.

Credit Suisse in July received a target letter from the US Justice Department notifying it that it was the subject of a federal criminal investigation into its offshore private banking services.

As reported earlier by Family Wealth Report, Switzerland is trying to agree to a deal with the US that would include its entire banking industry of some 355 banks. Swiss banking is a key component of the Alpine state’s economy, accounting for about 13 per cent of GDP.