Workers at the Grangemouth oil refinery will hold a rally outside the plant tomorrow amid a continuing dispute over the future of the site.
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.
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 the dispute.
Unite said MPs and other supporters will join workers at the rally.
Pat Rafferty, Unite's Scottish secretary, said: "Rather than demonstrating, workers want to be working to make sure that Grangemouth has a successful future. Instead their livelihoods are being thrown into turmoil because of Ineos' irresponsibility which risks the future of the site.
"Anger is growing among workers and the company now risks destroying good Scottish jobs and a powerhouse of the Scottish economy.
"Our message is clear; we will not give in to the threats and menaces of Ineos. We urge the people of Scotland to support us in defending the future of Grangemouth and the livelihoods of a loyal workforce, decent men and women now being stalked by fear.
"Once again I call on Ineos to drop the cynical blackmail, start the plant up and talk seriously about securing a future for Grangemouth."
The company said the dispute 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.