Two multinational coal giants have taken the highly unusual step of threatening legal action against union workers involved in a pay dispute with a different company.
Train drivers who work for Pacific National Coal - a division of the company Asciano, Australia's largest rail freight and port operator - are threatening to go on strike after salary negotiations collapsed.
Now, Xstrata Coal NSW, which is not involved in the salary negotiations, is threatening to take legal action against the workers if they go on strike. The threat was outlined in a letter to the Rail, Tram and Bus Union (RTBU).
In the letter, Xstrata's chief operating officer, Ian Cribb, wrote that his company had contracts with Pacific National for rail freight of 30 million tonnes of coal each year from its mines in the Hunter Valley and Tahmoor.
"If any industrial action is organised by the RTBU, and engaged in by its members employed by Pacific National Coal, it will cause significant harm to the business of Xstrata Coal," he said.
"Xstrata Coal is entitled to take all necessary steps to prevent any harm to its business.
"This may include the commencement of proceedings in a court or tribunal to stop or prevent industrial action from being taken without further notice to the RTBU."
A third company, Whitehaven Coal, has also threatened to make a complaint to the Fair Work Commission.
The union's national secretary, Bob Nanva, said it was "unheard of" for a third party, not directly involved in an industrial dispute, to threaten legal action. He said the strike action would be protected, having been approved by Fair Work Australia.
"This is a co-ordinated assault on the right of union members to collectively bargain and strike," he said.
University of Sydney Emeritus Professor Ron McCallum, who specialises in industrial law, said it was unlikely the union could be successfully sued if it was taking protected strike action, unless it had failed to satisfy all legal requirements under the Fair Work Act.
Pacific National's NSW coal division has been in negotiations over a new enterprise agreement for 12 months. The union said most of its members were on annual base salaries of $63,000.
A spokeswoman for Asciano said its coal division has been negotiating in "good faith" with the RTBU and was keen to finalise a new enterprise agreement.