STRASBOURG - More than 1,000 factory workers in eastern France agreed to a salary freeze and reduction in days owed as part of conditions imposed by General Motors Co GM.N to keep a car plant open.

The Detroit-based automaker had originally put the plant up for sale in 2008 at the height of the financial crisis to help raise cash to avoid bankruptcy, but failed to complete the transaction.

The Strasbourg factory was placed under the Motors Liquidation Co, the entity charged with selling off GM's unwanted assets to reduce its debts.

After emerging from bankruptcy in the summer of 2009, the firm opted to buy back the unit, which produces automatic transmission systems for GM and BMW cars.

On July 16, it offered to repurchase the plant for a symbolic euro and on condition that costs fall by 10 percent. .

Seventy-percent of 1,150 workforce approved the new measures, which includes a salary freeze for two years and a reduction of time off taken for accumulating extra hours.

Roland Robert, a spokesman at the CGT trade union, said the workers had succumbed to management blackmail and the union would stand by its position to oppose the deal.

GM said it had proposed the takeover plan after comparing costs with its Mexican plant, which were significantly lower.

As part of the deal, GM said it would keep production volumes at current levels and launch new products for the plant until at least 2020.

Last year, a tyre plant in northern France witnessed some of the most vehement worker reaction to restructuring in the European auto industry, with angry employees trashing two of the plant's buildings and setting fire to tyres in front of the Paris bourse in protest. (Reporting by John Irish and Gilbert Reilhac)