The CBI on Wednesday called Loop Telecom, CEO Sandeep Basu, Chairman of Shyam group Rajiv Mehrotra, former telecom minister A Raja's brother A K Perumal and close aide Sadiq Batcha, for questioning in relation with the 2G spectrum scam.
CBI is likely to question all nine companies which were awarded 2G licences in 2007-08 before March 1.
The agency has already interrogated Reliance ADAG chairman Anil Ambani, Unitech MD Sanjay Chandra and Videocon chairman Venugopal Dhoot.
Shahid Balwa, managing director of DB Realty, which is in a joint venture with UAE-based Etisalat group, was arrested earlier this month.