California's attorney general is investigating methods used by Hewlett Packard to oversee the activities of certain directors after a media leak.
HP used a method known as "pretexting" to gather records
In a bid to discover which employee had leaked "confidential" reports to the press, HP hired undercover consultants.
The firm's counsel said HP's methods were "not generally unlawful" but could not say if the techniques used by outside agents complied with the law.
Hewlett Packard said it was "cooperating" with the enquiry.
The firm's investigation of staff members came to light in a Securities and Exchange Commission (SEC) filing, in which HP acknowledged using an outside company to look into the leaks.
HP started to investigate workers after "multiple leaks of confidential HP information, including the internal deliberations of its board of directors," from 2005.
The investigations revealed that former board member George Keyworth had been the source of the leaks.
In May, Mr Keyworth stated that he had leaked information but refused to step down, despite being asked to.
The firm said it would not renew Mr Keyworth's position on the board.
Around the same time, HP director Thomas Perkins suddenly left the firm, after his concerns that phone calls and emails had been recorded improperly.
The method, known as pretexting, is employed by investigators to obtain information whilst hiding the investigator's identity.
HP meanwhile said recording and eavesdropping had not taken place.