Protests by workers at Coal India Ltd on Tuesday hit output by about 56 per cent, a senior company official told Reuters.
The workers' strike over implementation of reforms including allowing 100 per cent foreign direct investment (FDI) in coal mining - which India approved last month to attract global miners to India - paralysed operations.
The company, which accounts for over four-fifths of India's coal output and employs about 300,000 people, registered a 30% attendance due to the strike. India depends on coal-based utilities for three-quarters of its electricity generation.
Coal India produced a total of 466,000 tonnes of coal on Tuesday, which compared to an business-as-usual production estimate of 1.05 million tonnes, the official said.