The deadline for accepting terms and conditions for workers at the Grangemouth oil refinery will expire today.
Hundreds of workers attended a rally at the plant yesterday as the dispute over the future of the site continues.
Owners Ineos have written to the workers asking them to agree to changes to pensions and other terms and conditions as part of a survival plan.
Union Unite has accused the company of giving workers an ultimatum of accepting worse pay and conditions or lose their job.
The plant was shut down last week as a result of a dispute with the company saying it had cost it £20 million on top of monthly losses of £10 million.
Ineos has warned that the plant will close in 2017 without fresh investment and changes to workers' terms and conditions.
Around 400 employees, some with children and family, attended a rally at the plant yesterday in heavy rain and heard from speakers from Unite and other bodies such as the Scottish Trades Union Congress.
Site convenor Mark Lyon was the first speaker and told the crowd: "This is far from a typical industrial dispute that we are dealing with here.
"There are old fashioned words that come to mid like fairness and equality, and that's what we want.
"Incredibly, our members have been served notice that they will be sacked in 45 days unless they bend to the will of Jim Ratcliffe's Ineos. This is a move to sack one of the most skilled workforces in the country.
"It's crazy and we wont let it happen on our watch."
On Saturday, Scotland's First Minister Alex Salmond repeated a plea for unions to agree to no industrial action and management to reopen the site in order for negotiations to take place.
Ineos has said it needs an assurance that there will be no industrial action due to "safety concerns" about restarting the site.
Speaking at the rally, Pat Rafferty, Unite's Scottish secretary, said: "We welcome the First Minister's intervention and we say that there will be no industrial action to allow negotiations to take place for however long it takes.
"The company now needs to get back to the table, as the First Minister has called for, to stop this imposition and negotiate, and that's in all our interests."
The rally came on the day Unite published a strongly-worded advert in a number of Scottish newspapers titled ''a message to the people of Scotland''.
The union said Grangemouth is the ''powerhouse'' of Scotland's economy and urged management to open the plant.
It described Ineos as ''out of control'' and accused it of ''waging a campaign of fear against its employees''.
Ineos wants workers to respond to the proposed changes by 6pm today before considering the future of the site.
In an interview with the Sunday Times, Ineos chairman Jim Ratcliffe said: ''This is not a bluff. The clock is ticking, Grangemouth could have a future but that is absolutely in the hands of the workers.
''Raw gas is declining at a rapid rate and we cannot run the plant flat out.
''The situation is very serious but I want to emphasise that there is light at the end of the tunnel. Grangemouth can have a potentially exciting future.''
Mr Rafferty said: "It's the company that set this deadline so we're not quite sure what happens after that. We still believe there is time for it to be called off and to get back to negotiations, as has been called for.
"We're recommending to our members that they do not opt in and sign this offer, we want them to reject it and then get it back to us and we can negotiate with Ineos."
Ineos said more than 250 workers had so far accepted the new terms and conditions ahead of today's deadline, which it viewed as a "positive" development.
The company sent out a letter on Thursday to all 1,350 workers at the site asking them to indicate their support or rejection of the company's plan by 6pm today.
By the end of Saturday, more than 250 positive responses to the firm's survival plan had been received.
Calum MacLean, chairman of Ineos, said: "Whilst it's early days, the initial response to the survival plan has been pleasing.
"We weren't expecting many returns before Monday so we are taking this is a positive development."
Workers who accept the company's proposals will receive a transitional payment of up to £15,000 which the company said they can use as they wish, plus an enhanced employer contribution to their money purchase pension scheme.
Unite's Pat Rafferty said: "This is another crude attempt by Ineos to intimidate the workforce.
"They have deluged people with emails and letters - the pressure this company is putting on this workforce is phenomenal. But if after all this effort they can claim only one in every six backs their plans, we strongly urge them to rethink."