Around 100 miners at the last deep pit in Wales, Tower Colliery, walked out after a row with managers who told two employees to change their work schedule.
The colliery, near Merthyr Tydfil, became a workers' cooperative five years ago. When it was put up for sale in 1995 after British Coal said it should close, 239 of the pit's workers chipped in £8,000 each from their redundancy money and kept it open.
Tower was traditionally one of the most militant collieries in Britain - absolute solidarity made a picket line unnecessary during the strike of 1984-1985.
The latest trouble surfaced when coalface workers were told they would be transferred to another part of the mine to carry out dust suppression work. They refused, prompting a walkout by the morning shift early yesterday.
Officials for the National Union of Mineworkers urged miners who were due to clock on for the afternoon shift to resume work. But at a meeting in the pit canteen they also decided to strike.
Face workers at Tower earn around £400 a week. Annual bonuses are distributed and at the end of the first year there was a £3,000 payout.
Tyrone O'Sullivan, a director of the cooperative and a former NUM official, said: "There comes a time when men have got to grow up.
"This is the first time muscles have been flexed at Tower since we took over. Under British Coal there would have been an agreement to enable work to continue."
Mr O'Sullivan said production had stopped, although coal already brought to the surface was being delivered to customers.
He added that the two workers had been told to do jobs that they were trained to do, but refused and then decided to go home.
He said about 14 workers left the morning shift yesterday in support and most of the afternoon shift also went on strike.
About 80 of the colliery's 400-strong workforce were working to provide orders for the pit's two main customers, including Aberthaw power station, he added.
Mr O'Sullivan said: "The union is discussing it with the men and we are waiting for them to come back. I think the men will resolve this. They will realise what's happened and how silly they have been."
The pit produces up to 3,000 tonnes of coal a day.
The survival of Tower is important in an area largely untouched by the electronics era. Unemployment in the valley is around 10% and health and housing problems abound.
It is estimated that without the colliery the local economy would lose up to £10m a year.
The success of the mine has attracted widespread praise. The workers' buyout was even recently turned into an opera.
