Four-hundred workers at Holden's Elizabeth car plant in Adelaide have taken voluntary redundancies and will finish work on Friday.
The future of Holden in Adelaide is still in doubt with the company expected to finalise its business plan in September.
Federation of Vehicle Industry Unions spokesman John Camillo says more than 500 workers put their hands up to take a separation package.
"It's a better situation than the situation of people being forced out the door with no choice whether they want to stay or not so, it's a good outcome for all, but it's a sad day for those 400 people," he said.
The redundancies come as independent expert Goran Roos conducts an investigation into Holden's books and manufacturing practices.
Mr Camillo says Professor Roos is expected to give an update on his findings this week.
"Professor Goran Roos will speak to all the shop stewards in regards to his findings and what he's found in regard to the company opening its books and cost structures," he said.
"The real issue will be at the end of July when the recommendation of his findings will be put to Holden and the Federation of Vehicle Industry Union." On Thursday, (FBT), saying they could have a significant impact on the market for locally made new cars.
The Government announced the plan this week in an attempt to save $1.8 billion to offset the cost of moving from the fixed carbon price to a floating price a year early.
The changes mean drivers who buy cars using salary sacrifice schemes will have to keep detailed log books, breaking down their personal and business use.