after the company told senior staff it would stop making the iconic Commodore.
Job losses could start early next year with up to 350 staff losing their jobs by mid-2013.
Association of Professional Engineers, Scientists and Managers chief Chris Walton said senior Holden staff were told the 2014 Commodore could be the last made in Australia.
Mr Walton said the union, which represents engineers who design the Commodore, was told of the possible changes while negotiating a new pay deal.