The probe by CBI comes amid a major crackdown by department of telecom and its PSUs, which have imposed stiff penalties that have been challenged by Reliance Infocomm.
The CBI, which has initiated the probe suo-motu, has asked the authorities concerned to furnish relevant details of international telecom traffic, which is alleged to have been re-routed as local calls to avoid payment to levy to telecom PSUs, CBI officials said.
The investigating agency stumbled upon the case during its investigations in the illegal telephone exchanges busted in Tamil Nadu, Kerala and Andhra Pradesh recently during the agency's special drive on February 2.
CBI officials said that during its investigations into the functioning of illegal exchanges in the Southern states, it had found involvement of certain private telecom companies and some officials of department of telecommunications.
The official said the companies had been asked to provide relevant details to the Economic Offences Wing of the CBI.
The officials, however, clarified that no case has been registered against Reliance and other telecom companies.
According to CBI, the illegal operators were maintaining parallel telecom networks over and above the licenced networks. The loss of revenue is to the tune of a few hundreds of crore to the government of India as well as to the PSUs.
Apart from revenue loss, these illegal channels were also a security threat to the country as anti-national elements could use these channels which could not be policed by the law enforcing agencies.
Secondly these channels were being used to avoid payment of Access Deficit Charges. Earlier, DoT had imposed a penalty of Rs 150 crore (Rs 1.5 billion) on Reliance Infocomm for violating the licence terms and conditions by illegally rerouting international calls as local ones.
The penalty was challenged by Reliance Infocomm in the TDSAT. Hearing in the case has been completed and judgement has been reserved.
Similarly, the two telecom PSUs-- MTNL and BSNLhave raised a demand of over Rs 550 crore (Rs 5.5 billion) on Reliance and part of which has already been paid by the company.