The world's largest mining company, BHP Billiton, has launched legal action against the Maritime Workers Union over what it says was an illegal strike in WA's north west earlier this year.
The miner has lodged a writ in the Supreme Court seeking damages of up to $7 million over a strike by tugboat operators in Port Hedland in March.
The company claims the stoppage was instigated by MUA branch secretary Will Tracey.
It says Mr Tracey spoke to tug operators and instructed them to stop work for four hours.
BHP says that was a breach of their labour agreement with their contracted employer, and was therefore unlawful.
The company says it incurred additional expenses and suffered irrecoverable damages because of the stoppage.
The MUA says it will vigorously defend the lawsuit but has declined to comment further.