The probe is to investigate if Textiles Minister Dayanidhi Maran, a member of leading government ally DMK party and a former telecoms minister, coerced the founder of mobile phone firm Aircel to sell off his stake, the lawyer said.

Maran has in the past denied allegations he threatened or forced C. Sivasankaran, the founder, to sell off the stake to a firm considered close to the minister.

“Dayanidhi Maran is under the scanner, probe is going on,” K.K. Venugopal, lawyer for the Central Bureau of Investigation,told the Supreme Court. “There was an element of coercion.”

The move may further strain relations between the ruling Congress party and DMK, whose 18 lawmakers give the coalition government a narrow majority in parliament. But with the DMK out of power in its southern stronghold state of Tamil Nadu, few expect it to pull out of the government.

The case has already claimed another former telecoms minister, a DMK lawmaker and several business executives, who are all in jail pending trial and who have denied any wrongdoing.

A raft of corruption scandals in Singh’s second term has paralyzed policymaking in Asia’s third-largest economy and diverted attention away from nurturing sluggish growth and pushing forward much-needed economic reforms.

The telecoms scandal is over rule breaking and graft over a decade in the grant of lucrative telecoms licenses in the world’s fastest growing telecoms market.

In 2007/08 alone, such violations may have cost India $39 billion in lost revenue, a sum equivalent to the annual defense budget, the state auditor has estimated. The Supreme Court is monitoring the investigation of the case.

Maran’s party colleague Andimuthu Raja was telecoms minister during that period and Raja has been in jail for months.

Maran was telecoms minister between 2004 and 2007. He returned to the cabinet in 2009.