The workers, joined by Collie residents, began the work stoppage at 4pm on Tuesday. Premier Coal is the main supplier to the state-owned Muja and Collie power plants, which the WA government has promised to close by 2030.
Mining and Energy Union district secretary Greg Busson said workers were opposed to proposed roster changes that could result in staff losing about $30,000 a year in penalty rates. The union estimates the average annual salary at about $150,000, with more than 90 per cent of the mine's workforce unionised.
Workers currently operate 12-hour shifts on a four-days-on, four-days-off, four-nights-on, four-nights-off rotation. Mr Busson said two of the proposed rosters would effectively end night shifts and associated penalties.
"The worst [roster] is 8.5 hours all-day shift, Monday to Friday, because they lose all their penalties for weekends and night shift," he said.
While Premier Coal has offered a twelve per cent increase spread over four years, Mr Busson said the union wanted any increase front-loaded.
A Premier Coal spokesperson said the company was committed to reaching a fair agreement. "Premier Coal has participated in good faith negotiations throughout the enterprise bargaining process," the spokesperson said. "Our focus remains on the safety of our workforce and the continuation of safe and efficient operations."
Mr Busson said the $150,000 salary might seem generous, but the work was often dangerous and the pay was less than that taken home by coal workers in other states. Workers are also anxious about future employment in Collie as the region's coal industry winds down.