BHP Billiton is taking legal action against the Maritime Union of Australia over what it claims was illegal strike action.
The miner is seeking damages of around $7 million over work stoppages carried out by tugboat operators at its Port Hedland operations in March, the ABC reports.
However, it has not elaborated what the allegedly illegal strike was over.
BHP claims that the industrial action was caused by MUA branch secretary Will Tracey, who told the tug boat workers to strike.
The miner states that it was a breach of their labour agreement with BHP, and thus illegal, adding that it incurred expenses and damages due to the strike.
This is not the first time tugboat workers have carried out work stoppages at BHP's Port Hedland operations.
Late last year maintenance workers and crew from BHP contractor Teekay Shipping carried out industrial action after asbestos was discovered on a tug.
MUA assistant branch secretary Will Tracey said the Teekay crew were exposed to asbestos for up to 24 hours after the Star Voyager maintenance.
He said at least one worker had also exposed their family to asbestos after returning home from work in contaminated workclothes.
Yesterday thousands of workers, including those in the MUA, marched against enterprise migration agreements on mining projects.
About 5000 people marched up Hay Street to the West Perth headquarters of Gina Rinehart's Hancock Prospecting in protest of the private company's move to bring 1700 foreign workers onto the Roy Hill project in the Pilbara on an enterprise migration agreement.
MUA deputy national secretary Mick Doleman said the rally was not against foreign labour as blanket policy, rather, the unions wanted to see more done to train and employ Australians.
The MUA is preparing to fight BHP's lawsuit.