Mr O'Neill said Hastings workers had reported being offered substantial bonuses to work in McCain's Ballarat plant, where workers were on strike after a breakdown in collective agreement (EBA) negotiations and the company move to use contractors instead of employees.
He said McCain's Ballarat and Timaru plants were highly unionised but McCain Hastings did not have a collective agreement.
"On average the non-unionised McCain workers are paid significantly less."
While a trip to Australia might appear a good deal for workers, he said undermining striking workers was short-sighted.
Hastings plant manager Jeff Hope said two employees had been asked to travel to Australia to help run McCain's potato plant in Ballarat this week.
"Our employees in Ballarat are 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 we're offering," he said.
He confirmed E Tu was prevented from posting items on its Hastings notice board.
"Our company protocols would never allow for a non-employee to post unsubstantiated allegations from an Australian union in our plant here in New Zealand."
A Ballarat worker's forearms were recently treated in hospital for burns after a pipe burst at the plant.
The Australian union blamed the burns on untrained strike breakers but the company said the workers were fully qualified and staff assignments in different plants were a normal part of company operations.
McCain is a Canadian company and the largest processor of frozen potatoes in the world, processing other vegetables and pre-prepared meals.
Its $19 million plant upgrade in Hastings was officially opened by Prime Minister John Key in 2011.