Hundreds of workers at BiFab are expected to be given redundancy notices today.
Union leaders say they are 'dismayed' the struggling manufacturer is closing, despite the commitment shown by its workers.
They staged a 'work-in' late last year when the company was on the verge of entering administration over cash flow problems.
Members of the Unite union say the sites in Fife and on Lewis are now at risk of turning into an 'industrial graveyard'.
Management at the yards told trade unions yesterday that they will be issuing redundancy notices to the core workforce on Tuesday 13th, giving 45 days notice of the closure of the yards.
Some 260 jobs are to go by early summer with the possible closure of the yards completely by the end of June.
Unite’s regional officer Bob McGregor says:
"So much has been done to save these yards until now.
"The workers there have fought for their future and it is difficult to believe that it can now be snatched away from them.
"The closures of these yards will turn these areas into an industrial graveyard.
"The prospect fills us with dismay.
"In November last year the BiFab yards were threatened with closure as the company appeared to be running out of money as a result of a payments dispute with a major sub-subcontractor on the Beatrice Wind farm contract for the Cromarty Firth.
"The workers at BiFab occupied the yards and called for Scottish Government intervention to save them.
"The Industry minister Keith Brown and the First Minister, Nicola Sturgeon, eventually managed to broker a deal involving all the major contractors to save the yards.
"However the Beatrice Wind farm contract is now coming to a close and BiFab is now running out of work.
"There has also been open speculation that the yards may be taken over by a major Canadian concern.
"Although there has been no official confirmation of these moves.
"We can’t say this is a total shock because work at the yard has been running down for weeks now.
"However all the interested parties, the company, the contractors, the unions and the Scottish Government, given what has been done so far, must surely look to have an eleventh hour intervention which can do something to save these jobs."
The Unite union says BiFab's management told trade unions that the first redundancies would start in May and the closure would be completed by the end of June.
The union is warning these timescales can only be reversed if new contracts can be established for the yards.