The action would be the first strike in the Pilbara in decades, and the alarms were sounding for those in the mining industry around pending industrial action as far back as March.

BHP could lose $100 million in revenue a day if two unions vote for work stoppages, unless it can find about 450 replacement staff in Western Australia.

Unionised workers at BHPs operations in Port Hedland could walk off the job as soon as next week after endorsing protected industrial action.