The company accounts for about 80 percent of India's total output and worker strikes have previously crippled power plants. Coal fuels 60 percent of the country's power production.
The five worker unions of Coal India will go on a strike from Tuesday against the government's plan to allow private companies mine and sell coal, said Jibon Roy, general secretary of the All India Coal Workers Federation.
The unions might again go on strike on January 13, Roy said.
To cover for the loss from the strike, Coal India has been transporting coal in 225 trains over the past few days instead of 207 per day, said one of the officials, both of whom did not want to be named as they are not authorised to talk to media.
A train, called a rake by the commodities industry, can transport 4,000 tonnes of coal per day.
But with a fifth of India's 100 power plants monitored bthe Central Electricity Authority running on coal stocks of less than 4 days, the strike could still aggravate the shortage and lead to power cuts in parts of the country.
This could also boost shipments into India, the world's third largest coal importer.

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