The US tax agency on Monday filed with Swiss authorities for administrative assistance on information related to 4,500 bank accounts, following a deal reached between the two governments earlier this month.
The out-of-court settlement required that the country's largest bank UBS AG hand over to US authorities information on accounts that are believed to belong to clients who hid their assets from the Internal Revenue Service to avoid paying taxes. Swiss confidentiality laws generally mandate that banks are not allowed to divulge client information.
Under the Aug 19 agreement, the first 500 names must be processed by the Swiss Federal Tax Administration (FTA) within 90 days. The Swiss would have one year to process the request for the rest of the accounts.
According to a government statement, the FTA would investigate the accounts with legal and tax experts and issue a conclusive decree on surrendering the information within the two time-frames.
The 4,450 accounts - estimated to hold some $18 billion - will come on top of data of some 250 accounts that was already handed over in February, when UBS also agreed to pay a fine of $780 million.
UBS has admitted its employees helped clients evade paying taxes, in some cases committing fraud.
The deals in the UBS cases have been seen as blows to Swiss banking secrecy. Bern has also started to renegotiate and sign new bilateral double taxation agreements with other countries, based on transparency rules of the Organization for Economic Cooperation and Development.
The government statement said persons concerned would be allowed to file appeals with Swiss courts.
Also Monday, Bern said it knew nothing about statements by a French minister who told a newspaper that Paris had obtained confidential data on some 3,000 bank accounts in Switzerland.
It was unclear how France had acquired the data.