Some 150 workers at the mining giant's bulk export terminal in Western Australia's Port Hedland are taking part in the new series of strikes, following a walk-out in July.
That eight-hour stoppage was the first major industrial action to hit the resource-rich Pilbara region in decades, with estimates it may have cost BHP $50 million in lost revenue and the state $6.8 million in royalties.
"This action is the direct result of the company's failure to negotiate seriously," Australian Manufacturing Workers Union WA state secretary Steve McCartney said on Saturday.
Workers felt they had been left with no choice, he added.
"BHP has made it clear it can move quickly when its operations are affected. It now needs to show the same urgency at the bargaining table.
"The company can end this dispute at any time by putting forward a genuine offer that respects the skill, experience and contribution of its workforce."
The two-day strike will consist of a 24-hour ship-loading ban followed by a 24-hour work stoppage from 5.30am on Sunday, with members of the Electrical Trades Union, the Western Mine Workers' Alliance and the Australian Workers Union all participating.
High voltage and power workers, who are negotiating a separate agreement with BHP, will down tools for 12 hours on August 9.
About eight ships are expected to finish loading from BHP ports over the weekend, a source familiar with the matter said.
BHP has previously said plans are in place to minimise any potential operational disruptions.
Western Mine Workers Alliance spokesperson Craig Beveridge said unions had given BHP ample opportunity to respond to concerns.
''Instead of engaging in the bargaining process, BHP continue to delay, distract and waste time," Mr Beveridge said.
BHP accused unions of failing to engage in good faith, pointing to its offer of a 16 per cent pay increase over four years as proof of its own efforts.
"BHP is frustrated by the lack of progress in bargaining and concerned about the lack of genuine engagement from the unions in bargaining meetings," a spokesperson said.
Nationals' state leader Shane Love, also shadow minister for mines and petroleum, said both parties must continue negotiating in good faith.
''A prolonged dispute helps no-one. It would be workers, employers and Pilbara communities that ultimately bear the consequences of any return to the entrenched industrial conflict of the past.''
Bargaining for a new pay deal for 450 operators and maintenance workers began in October 2025 amid record share prices and rising cost-of-living pressures.
About 577 million metric tonnes were exported from Port Hedland in 2024/25, worth an estimated $115.8 billion.
The unions are next expected to meet with BHP on August 18, the same day the mining giant will report its annual results.
Mr McCartney said workers were striking instead of waiting for the next meeting in order to show BHP they're serious.
"We're sick of being stonewalled. We want to show them ... that we can take serious action if we have to."
He also said the potential of further action down the line was a question for BHP.
"If BHP are going to sit around the table honestly and do a transparent deal ... then I think we'll all be feeling better."
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