Raja, who is in Chennai, was served notice at his official residence under section 160 of Criminal Procedure Code to appear before the agency for questioning.

Under the Section, a person is asked to join the investigation and share all information that he or she may have about a case.

It was not clear as to when Raja has been summoned by the CBI. The premises of Raja, Baijal and Radia were searched by the investigating agency earlier this month in connection with the case.

Following allegations relating to the 2G scam, Raja had on November 14 resigned as Telecom Minister.