Swiss newspaper SonntagsZeitung reported earlier the bank's action was in connection with a U.S. investigation into Credit Suisse's Israeli unit over possible tax evasion.
"Credit Suisse is carrying out an internal investigation relating to tax matters," the bank said in a statement. "The review is focusing on employee conduct."
Media reports first surfaced in June that the U.S. Department of Justice was conducting a probe to determine whether Credit Suisse employees in Israel helped dual Israeli and U.S. citizens to evade American taxes.
Credit Suisse did not comment on further details of the investigation.
(Reporting by Brenna Hughes Neghaiwi; editing by Clelia Oziel)