The Unite union called on Grangemouth workers yesterday not to cave in to the oil refinery bosses' "menacing" tactics to sign away their rights and said it was considering legal action.

Workers at the massive oil refinery were yesterday given details of owners Ineos's "survival plan," with the firm saying it was "D Day" for the site.

The company told workers they could lose their jobs and be re-employed on poorer terms unless they agreed to give up their final-salary pension, as well as accepting pay freezes and pay cuts by 6pm on Monday October 21.

It said it was by-passing the union and going directly to the workforce, amid fresh clashes with Unite over the company's finances and its decision to close the plant.

But Unite, which has called off a 48-hour strike scheduled from Sunday, accused Ineos of using "fancy accounting manoeuvres" to "cynically blackmail" the staff.

The union challenged the firm's statements about the financial difficulties it faces and said it was looking to take legal action over Ineos's "sign or be sacked" ultimatum.

Ineos claimed that the dispute with Unite over the treatment of union convener Stephen Deans had cost it £20 million at a time when Grangemouth was losing £10m a month.

Mr Deans was suspended by the firm as a result of the row over the selection of a Labour candidate in Falkirk. He was later reinstated, but is facing an internal investigation by the firm.

Ineos chairman Calum MacLean said shareholders had "expressed extreme concern" over the cost of the recent industrial action, adding: "The site cannot afford this - hence the urgent need for employees to decide to support the company."

But Unite's regional secretary Pat Rafferty blew a hole in the claims over its finances. He said an analysis of the firm's accounts commissioned by the union suggested that Ineos expects to make profits of half a billion pounds in the coming years.

He accused the firm of attempting during recent Acas talks to force the union to sign a legally binding agreement backing its assessment and prevent the union publishing its own analysis.

"This attempt to tie our hands has only increased our suspicions that Ineos is using fancy accounting manoeuvres to pull the wool over the country's eyes and treat us with contempt," he said.