General Motors subsidiary Opel has given unions at the threatened plant in Antwerp until mid-April to agree to finalise a social plan for all 2,600 workers at the Belgian factory.

Three unions put forward suggestions earlier this month to try and prevent Opel closing the plant entirely, with the GM division indicating this could see the Astra TwinTop coupé convertible produced there.

"The main issue is that management is putting a deadline to find an investor to the end of September," an Opel spokeswoman in Antwerp told just-auto.

"But the proposal has a few elements and conditions, for example we have to finalise a social plan for all 2,600 workers by mid-April. In a first phase, 1,250 people might be leaving. If we don't find an investor then the social plan will also be applied to the rest."

Opel said some "spontaneous" demonstrations took place this morning at the Antwerp plant following yesterday's meeting at the manufacturer's European headquarters in Russelsheim of workers wanting "clarification" on any potential alternative plans.

The Opel spokeswoman added the automaker was willing to "put some efforts" into the proposals, details of which remain unclear, and that it would have a working group evaluate any potential investor.

"We will meet very regularly to have a well-balanced plan," added the spokeswoman.

Belgium's Loi Renault rule allows unions to put forward proposals once a facility closure is announced.

Opel unions were not immediately available for comment.

Unions silent on rescue plan