About 500,000 Indian coalminers start a five-day strike today. The miners, employees of Coal India, which accounts for four-fifths of national production, object to looming change in a notoriously corrupt and inefficient industry. Last year, after a scandal known as “Coalgate”, the Supreme Court cancelled most mining licences issued to private companies between 1993 and 2010. The government plans speedy auctions of new licences, to encourage competition: the first 23 are supposed to be completed by March. Some unions suspect privatisation by the back door. Even though Coal India remains largely state-owned and state-run and is likely to be reformed only gradually, the strikers want to show that they will fight further changes to their own firm. Many power stations are said to have less than four days’ worth of coal, despite stockpiling. If the lights go out, the determination of the prime minister, Narendra Modi, to reform India’s economy will face its biggest test yet.