The union representing rail workers has threatened to take legal action against Pacific National Coal, accusing them of bribing workers to avoid strikes.
Pacific National Coal and the Rail, Tram and Bus Union have been locked in a pay dispute for more than 12 months.
The company has taken the unusual step of offering to guarantee a 4 per cent pay rise to individual workers who promise not to undertake industrial action.
The union's national secretary Bob Nanva says that is discrimination, and a breach of the Fair Work Act.
"This is an unprecedented and disgraceful attempt to bribe our workers," he said.
"This is an attempt to bribe and bully the workforce into not exercising their legal right to strike.
"Every member who participated in the ballot has a legal right to take protected action and this is an attempt by Pacific National to subvert what is a legal process.
The union is seeking a 9 per cent pay increase.
However, Pacific National is warning that its current offer will be reduced to 3 per cent if an agreement is not reached.
And it will be cut further if the dispute continues for another month.
The company says it has held many meetings with the union, but it was now apparent that the bargaining process had been exhausted.
In a statement, Pacific National says it has been approached by a number of employees who want to accept the four percent deal.