So far, the right to commercial mining was reserved for Coal India.
"The working committee has already decided on a strike if the Bill is passed. The moment it happens, we will give a call for strike," said Jibon Roy, general secretary, All India Coal Workers Federation.
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Another Left-leaning union, Indian Mine Workers' Federation (affiliated to the All India Trade Union Congress), said it was mulling joining the strike. "We are discussing internally. But in no way are we going to accept the passage the Bill," said Ramendra Kumar, secretary, Indian Mine Workers' Federation.
Three other unions - Congress-backed Indian National Mineworkers Federation (INMFW), Hind Khadan Mazdoor Federation and coal workers' union of the Bharatiya Mazdoor Sangh - are yet to make their stand clear.
While all the unions claim to have more than 100,000 workers' strength, sources say INMFW is the leading union in terms of support base, representing about 30 per cent of the total 350,000 workforce of CIL. The other four unions' support base is between 15 per cent and 25 per cent.