Holden has denied union claims that the design and engineering of the iconic Commodore is likely to be moved overseas.
The Association of Professional Engineers, Scientists and Managers Australia (APESMA) has said Holden had advised it was "highly likely" the Commodore would be engineered and designed overseas after 2014.
The shift would cost 360 engineering jobs in Australia and thousands of job losses in the related auto supply manufacturing industry, APESMA has said.
However, General Motors Holden Australia director Mike Devereux has denied this and described the union comments as disappointing.
He said Holden did have discussions with the union about possible options available to the car manufacturer in the future, but it had not made any decisions yet.
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"The back half of this decade ... is frankly anybody's guess. As to what it is Australian customers are going to want to drive in 2016, 2017, that's what we're trying to plan right now," Mr Devereux said.
He said the union's comments to the media were not only "strains of half-truths" but also damaging.
"It's illogical if the union's goal is to secure the bright future of jobs and investment in this country. What we're seeing today in the newspapers is the opposite of helpful," he said.
APESMA chief executive Chris Walton said Holden should be able to confirm the future of the Commodore because of the planning time needed in manufacturing the car.
"They would have to make decisions in the next few months," Mr Walton said.
"What they're trying to, unfortunately, suggest to the community is you don't have to worry about that until 2014, when in fact we need to worry about it now."
He said that because of the lead time in car design, job losses could commence early next year.
"We hope Holden will come out and confirm that they will engineer and design the post-2014 model in Australia.
That would be the best outcome," Mr Walton told AAP. Mr Devereux gave an assurance earlier on Thursday that the Commodore would be a fully Australian product for a long time to come.
"All I can tell you is that Holden is, for example, the Commodore, 100 per cent designed, engineered, manufactured in Australia today, and the next Commodore, 100 per cent designed, engineered, manufactured in Australia, for many, many, many, many more years," he told ABC radio in Melbourne.
One thing the union and Holden do agree on is the need for the Australian government to take action.
"The Australian government has historically co-invested in vehicle companies and we support that and we suggest that should tie that money to a commitment from Holden to keep the engineering and design in Australia post-2014," Mr Walton said.
Mr Devereux said it would also welcome co-investment from the government.
"Australia needs to fight for its right to make things like automobiles in this country," he said.
Victorian manufacturing minister Richard Dalla-Riva said the speculation was unwarranted, premature and occurring amid enterprise bargaining negotiations. Richard Dalla-Riva said Holden had given a positive commitment to the government and manufacturing in Victoria.
