More than half of the 450 workers at BHP's bulk export terminal in Western Australia's Port Hedland downed tools on Thursday over a wage dispute.
It's the first major industrial action to hit the resource-rich Pilbara region in decades amid estimates it could cost BHP $50 million in lost revenue and the state $6.8 million in royalties.
The workforce wants standardised pay rates and locked-in terms and conditions, Electrical Trades Union WA secretary Adam Woodage says.
"Workers have exercised their legal right to walk off the job," he told reporters on Thursday.
"These workers have not taken this lightly.Â
"They know this is a historical moment."
Mr Woodage said it would cost BHP nine cents per ton of iron ore it exports or $25,000 per worker to end the pay dispute.
"Our message is clear ... if BHP do not listen to our members' claims, if they do not concede ground, our members may, will, instruct this union that they are willing to go on strike again," he said.
Mr Woodage said unions would continue to negotiate with BHP on Tuesday when more pay talks are scheduled in front of the Fair Work Commission.
He disputed claims that the strike would impact WA's coffers and future investment in the Pilbara.
"The iron ore that we have in this state of WA up here in the Pilbara region is not going to magically disappear," he said.
"There's always going to be a miner that wants to dig it up, crush it, export it, and sell it."
BHP said it was disappointed the unions pressed ahead with the strike and it would continue operations.
"We remain committed to bargaining in good faith," a spokesman said.
The company said it had tabled a draft agreement which included a 16 per cent pay increase over four years for the majority of employees, but Mr Woodage disputed the claim.
Premier Roger Cook said the industrial action was concerning but rare.
He called for the mining giant and unions to return to the bargaining table.
Mr Cook said he didn't think the industrial action would impact future investment in the Pilbara region and the state's broader resources sector.
"People respect that this is part of our industrial relations system," he said.
"There have always been negotiations between unions and the mining companies in the northwest.
"We continue to see very strong investment in the Pilbara from our resources industry and we'll continue to see it into the future."
WA Nationals Leader Shane Love said unions were growing more powerful in the state and exerting influence over the ruling Labor party.
The mining giant and combined ports unions failed to reach a wage agreement following a five-hour bargaining session earlier in the week.
The ETU, the Western Mine Workers' Alliance (Australian Workers Union) and the Australian Manufacturing Workers' Union are involved in the industrial action.
The stoppage will run for eight hours from 2pm to 10pm local time.
Earlier on Thursday, Electrical Trades Union members rallied outside BHP offices in Melbourne and Brisbane in solidarity with their WA counterparts.
Bargaining for BHP's port operations agreement started in October 2025.
The unions say BHP has failed to progress wage-bargaining talks for more than six months.
About 577 million metric tonnes were exported from Port Hedland in 2024/25, worth an estimated $115.8 billion.
The company said it paid $2.8 billion in state royalties and related government payments in the 2025 financial year, contributing about nine per cent of all WA government revenue.
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