New owners, Canadian firm D F Barnes, are set to cut 35 jobs – leaving just eight shopfloor workers for care and maintenance.
Trades unions have vowed to fight to save the yard.
The shock development comes less than three weeks the north American firm took over after extensive negotiations with the Scottish Government.
Senior executives from the Canadian firm told workers and their trade union representatives that statutory redundancy notices were being issued to 35 of the remaining 43 core staff at noon.
Joint Trade Union Secretaries Gary Smith and Pat Rafferty said: “The scale and speed of these redundancies was not expected.
“It means that some workers will be out of a job as early as two weeks time and most will be gone in three months. “But the trade unions will not be found wanting and our battle for BiFab continues. We knew the road ahead would be hard and the need for new contracts is obvious but clearly a major problem has emerged in terms of the future prospects for fresh work over the last fortnight.”
They added: “As a matter of urgency, we need to understand what those problems are and whether they can be overcome in the short term. We are working now with the employer and the Scottish Government to achieve this objective.”
Commenting on the redundancies notices that have been issued to employees at Bi-Fab, a Scottish Government spokesperson said: “The acquisition of BiFab by DF Barnes represents a significant step forward in our efforts to restore BiFab to its place at the centre of Scotland’s marine energy industry.
“But there is a lot of hard work ahead. As ministers made clear when new ownership was secured while the current contract comes to an end, and efforts go into winning new work, there will continue to be difficult times for the three yards.
“But the commitment of DF Barnes gives BiFab the best chance of winning future contracts and securing new work.
“Nonetheless, this announcement will be hugely concerning for the workers affected and their families – we are in regular contact with the unions and we stand ready to provide support through our Partnership Action for Continuing Employment (PACE) initiative.”
The spokesman added: “By providing skills development and employability support, PACE aims to minimise the time individuals affected by redundancy are out of work.”