US authorities are investigating whether Credit Suisse helped American citizens evade paying taxes.
The Swiss bank said it had been notified that it was a ''target'' for investigation.
Credit Suisse said it would cooperate with the investigation ''subject to Swiss legal obligations''.
In February, four Credit Suisse bankers were indicted for helping taxpayers hide money in secret bank accounts.
At the time, Credit Suisse said that it was not part of the investigation.
The Department of Justice previously threatened another Swiss bank, UBS, with legal action if it failed to hand over the details of 4450 US customers suspected of tax dodging.
In June last year, the Swiss parliament passed legislation permitting the banks to share customer details with US tax authorities.
The BBC reports UBS ended up paying a fine of $US780 million.
