The US Justice Department is investigating Swiss bank Credit Suisse over suspected tax evasion by wealthy American clients.
Credit Suisse said it will co-operate with US authorities within the limits set by Swiss banking secrecy.
"The investigation concerns historical private banking services provided on a cross-border basis to US persons," the bank said in a statement.
"It has been reported that the US authorities are conducting a broader industry inquiry," it added.
Credit Suisse is the most high-profile Swiss bank to be targeted by US investigators since rival UBS AG became embroiled in a tax evasion probe three years ago.
Zurich-based UBS admitted to helping US clients hide money on offshore accounts and ended up paying a fine and giving US authorities details on thousands of American account holders.
The case prompted Switzerland to ease its strict banking secrecy rules in response to international pressure.