Workers at the Ferguson shipyard at Port Glasgow have met at the site amid fears of job losses.
The GMB union says Scottish ministers must intervene
A shipbuilding union said up to 99 out of 126 workers would be made redundant, threatening the survival of one of the last yards on the lower Clyde.
About 70 employees attended the meeting and were told that unions would seek intervention by the Scottish Executive.
Ferguson said the yard would stay open, but is hoping to transfer staff to BAE Systems at Scotstoun and Devon.
Jim Moohan, chair of the Confederation of Shipbuilding and Engineering Unions, said 86 manual and 13 technical and managerial staff would lose their jobs.
"The news was worse than we thought as I have been advised that 99 staff are to be made redundant," he said.
"That will leave a very limited staff of around 30 left behind.
"This is very blunt and very damaging - the staff losing their jobs have no alternatives for re-employment."
He said he now feared the total shutdown of the historic yard within a year.
The Ferguson yard was threatened with closure two years ago when it lost a vital contract to a Polish rival.
Unions said the yard needed a £14m tender to build a fisheries protection vessel to safeguard its future.
Mr Moohan said: "It's really a very bleak outlook.
"We will be calling on the Scottish Executive to place this multi-million pound order at Fergusons to secure the future."
However, managing director Richard Deane insisted that the news of redundancies did not spell closure.
He said the exact number was still be decided, but it was unlikely that as many as 99 workers would go.
Mr Deane said: "We have been continuing to restructure the company - this is by no means a closure."
He said shipbuilding would continue at the yard and attempts would be made to relocate axed workers to BAE Systems, which confirmed that negotiations were taking place.
It is also thought the Port Glasgow yard will take on repair and design work.
However, local Labour MSP Trish Godman said she had submitted a written question on the issue and would be speaking to ministers to push the yard's case.
Scottish National Party enterprise spokesman Jim Mather MSP said that Scotland and its shipbuilding industry deserved better.
"It's time for a fresh approach to government in Scotland along with new thinking to deliver the real growth and economic muscle that Scotland require," he said.
Scottish Conservative leader Annabel Goldie said: "What is important now is how we help the beleaguered community of Inverclyde deal with the current economic challenges which have been exacerbated by this very unwelcome news."
Grahame Smith, general secretary of the Scottish Trades Union Congress, said: "These job losses highlight, once again, the need for the executive to adopt a strategic approach to public procurement.
"It is time the executive shed its institutional timidity in the face of all things European and stood up for Scottish industry."
An executive spokesperson said: "There are no current tenders for fisheries protection vessels.
"Following the identification of flaws in the previous tender process, the Scottish Fisheries Protection Agency said it would review its internal procedures.
"The SFPA will not retender until that review is completed."