Grangemouth's smokestacks hulked over a silent sprawl of machinery tonight as refinery owner Ineos's "sign or be sacked" ultimatum loomed.

The fates of hundreds of workers' jobs hang in the balance as the Morning Star went to press, just minutes before the company's deadline demanding their workforce agree to drastic cuts to pay and pensions.

The company told the refinery's 1,350 workers they had until tonight to consider new terms - including axing their final-salary pension, frozen wages until 2017, and cuts to shift allowances, overtime pay, holidays and redundancy terms.

Workers who don't sign up will face a 60-day legally mandated "consultation" period and then lose their jobs.

Meanwhile the company had shut down the plant's entire operations, which include processing 80 per cent of Scotland's petrol supply - and had no plans to reopen until their workers signed up to the new scheme.

Ineos's press office told reporters on Saturday they had counted around 250 signatories so far - refusing to update that figure yesterday.

But union Unite campaigns officer Peter Welsh told the Morning Star they had collected more than 600 forms unsigned at the union's site office by noon.

The lunchtime cache would already account for nearly half of the plant's entire workforce.

Ineos has ruled out any return to negotiations, telling the Star last week it had "reached the end of the line" with conciliation service Acas.

Instead it would launch the a 60-day consultation for mass redundancies.

But Mr Welsh told the Star a demand with no negotiation was no consultation at all.

"What you're effectively asking to do is sign away their statutory consultation rights. Whatever you feel about them, they're better than nothing," he said.

The company hijacked an industrial dispute over an internal investigation of Unite convener Stevie Deans to launch a wholesale attack on the union and the workforce.

Ineos claimed Mr Deans misused company resources to recruit employees to the Labour Party during the Falkirk selection dispute.

But he was cleared of any wrongdoing by the Labour Party, a police investigation and even an earlier Ineos probe.