New Zealand workers have been called 'scabs' for agreeing to be flown to Australia by food company McCain to to fill in for striking staff.
The union E Tū described the group as 'strike-breakers' and 'scabs' said it was 'disgusted' at their actions.
"If New Zealand workers think they won't be affected by what's happening across the Tasman, they're dreaming," said E Tū's National Industry Strategy Director, Neville Donaldson.
"They could be next if McCain in Australia succeeds in replacing good jobs with contractors."
The Australian Manufacturing Workers' Union is locked in a collective agreement dispute with McCain, the world's largest manufacturer of frozen fries.
McCain, through their Australian PR agency Porter Novelli, clarified nine New Zealanders travelling to Australia, rather than the 10 E Tū had claimed.
Two were travelling from its Hastings plant and seven from Timaru this week.
Australian Manufacturing Workers' Union organiser Angela McCarthy said they would provide cover for McCain's striking members at the company's Ballarat plant.
"They are undermining our lawful protected action to bring the company to the table and take our claim seriously," she said.
"Basically, anyone undermining another worker's action is a really low act."
E Tū said there were few McCain union members in New Zealand.
In a statement, McCain said the union appeared to be focused on using an Australian dispute as a vehicle to gain attention and try to gather members in New Zealand.
"It is cynical and extremely irresponsible," the statement said.
The company was putting its offer directly to employees to vote on since it hadn't been able to come to an agreement with the union despite good faith bargaining for six months, it said.
On the two Hastings employees helping run the potato plant in Ballarat, the company said workers at the plant had been "unable to work to full capacity while the union runs protected action".
"So some of our New Zealand employees are helping out while their Australian colleagues wait to vote on the EBA [enterprise bargaining agreement] we're offering. "