The Central Bureau of Investigation (CBI) on Friday filed charge sheet against three telecommunication firms, viz. Bharti Airtel Ltd, Vodafone India and Sterling Cellular Ltd, as part of its investigation into alleged corruption in allocation of excess spectrum during the NDA regime.

In the charge sheet, the investigation agency also named former telecom secretary Shyamal Ghosh. Filed under provisions of Prevention of Corruption Act, the agency estimated that the irregularities in the allocation of spectrum cost the exchequer around Rs 846 crore.

The excess spectrum was allotted on 17th of July 2002 to Bharti Cellular Ltd, Sterling Cellular Ltd and Hutchison Max, which are now known as Bharti Airtel, Vodafone Mobile Service Ltd and Vodafone India Ltd, respectively.

In its charge sheet, the CBI said Shyamal Ghosh, in conspiracy with then telecom minister late Pramod Mahajan, abused his position to extend undue favour to the three firms, causing loss of Rs 846.44 crore to the exchequer.

J. R. Gupta, former deputy director general of DoT and former director of BSNL, who was named in the FIR as one of the accused, has been made as one of the seventy-three witnesses in the case.

The court will consider the charge sheet on January 14, 2013.