Unite, the union, says it has agreed a deal with Magna to avoid any compulsory redundancies at Vauxhall plants.
It wants to protect jobs at Ellesmere Port and Luton.
The union said it had agreed to a two-year pay freeze and other cost-saving measures in return for no forced job cuts.
Magna declined to comment on the union's announcement.
The deal "gives both plants job security and a future through to 2013, providing a good basis for a long-term future beyond that", said Tony Woodley, joint general secretary of Unite.