Shares of Bharti Airtel have tumbled by 3.6 percent on Monday in the aftermath of Central Bureau of Investigation (CBI) raids on its offices and those of Vodafone''s.  

Bharti shares pared losses to trade 1.04 percent lower at 0644 GMT in a Mumbai market down 1.2 percent.

The CBI has registered a case against the companies, two former telecoms ministry officials and others, it said. The case relates to alleged irregularities in allotting mobile spectrum during the previous government led by the Bharatiya Janata Party (BJP), which is now in opposition.

Alleged "undue favour" shown to companies had cost the government about 5.08 billion rupees ($98 million) over 2001-2007, the CBI said on its website.

The CBI said the former telecoms ministry officials with approval of the then-telecoms minister took an alleged "hurried decision" on Jan. 31, 2002, to grant additional spectrum beyond 6.2 megahertz to the companies in violation of the report of a technical committee.

Pramod Mahajan, the then-telecoms minister, has been excluded from the case since he died in 2006.

"The market is not shocked by the CBI enquiry as it was expected since media reports were already suggesting that the agency could widen the scope for enquiry into telecom firms," said R.K. Gupta, managing director at Taurus Asset Management in New Delhi.

The Supreme Court, which is monitoring the probe into a 2007-2008 telecoms scandal that rocked the ruling Congress Party-led government, had asked the CBI to investigate any possible irregularities in the grant of licences from 2001 to 2007.