The Zurich Cantonal Bank is the latest Swiss bank to be targeted by United States justice authorities, according to reports.
The bank confirmed a report in the Tages-Anzeiger newspaper on Wednesday that it was on a US justice department list of banks suspected of helping US citizens evade taxes.
The Swiss Financial Market Supervisory Authority (Finma) had notified the bank of the investigation, it said.
On Monday, the American authorities announced that they were enquiring into the practices of eight unnamed banks.
swissinfo.ch and agencies