Credit Suisse is being investigated by the US Department of Justice as part of a broader inquiry into banks suspected of helping Americans evade taxes.
The investigation is in relation to historical private banking services across borders.
The bank said it received a a letter notifying it that a probe had been launched.
Credit Suisse said in a statement: "Subject to our Swiss legal obligations we will continue to cooperate with the US authorities in an effort to resolve these matters."
City A.M. Reporter