New Delhi, Aug 20 (IANS): Five trade unions operating in Coal India (CIL) and its subsidiaries have served a strike notice against a proposed five percent stake sale in the state miner, CIL said Tuesday.

"Five central trade unions operating in Coal India and its subsidiaries have served strike notice for three days with effect from September 23 to 25 against proposed disinvestment of 5 percent of CIL shares and other demands," CIL said in a filing with the Bombay Stock Exchange (BSE).

The five trade unions - Indian National Trade Union Congress (INTUC), Hind Mazdoor Sabha (HMS), Bharatiya Mazdoor Sangh (BMS), AICWF and All India Trade Union Congress (AITUC)- represent about 90 percent of CIL's 383,000-strong workforce.

CIL also said the All India Coal Workers' Federation (CITU) is understood to have decided to withdraw their three-days strike slated to start Sep 19, and join other unions in the strike beginning Sep 23.

CIL, the world's largest miner producing over 80 percent of India's coal, produced 452.21 million tonnes in 2012-13. The threatened strike is estimated to hit output to the tune of more than Rs.500 crore.