The New York Department Of Financial Services subpoenaed Credit Suisse last week as the regulator's tax evasion probe of the firm widens, a source told CNBC on Tuesday.
The subpoena sought e-mails, personnel files, travel records, expenses and other materials of employees of the company's New York office, the source said.
The New York Department Of Financial Services, which regulates the New York office of the Swiss finance firm, has been investigating whether the bank helped it's clients to avoid paying taxes.
Credit Suisse shares were trading slightly lower on Tuesday. (Click here to get the latest quotes.)