Nicola Sturgeon has challenged the Prime Minister after trade unions warned up to 800 shipyard jobs on the Clyde could be axed by BAE Systems.
The GMB said on Friday that unions have been warned of a "worst case scenario" of up to 800 job losses in the Clyde workforce if the UK government does not honour contracts to build frigates with the defence giant.
Unions have expressed fears that new work to build type-26 frigates for the Ministry of Defence, announced in February 2015, might now be delayed until 2017 - and that some of the work may even be transferred to other shipyards.
GMB Scotland secretary Gary Smith said: "This would be a total betrayal of the upper Clyde workforce by a desperate Tory government trying to shift the goal posts in the face of their failing economic stewardship.
"We've gone from the upper Clyde workforce being promised the manufacture of 13 Type-26 frigates in 2014, for that to be cut to eight frigates last year.
"We've gone from promised investment that would secure thousands of skilled jobs and hundreds of apprenticeships for a generation, only to be told to prepare for redundancies.
"In the same week that Scottish unemployment increased by 20,000, the prospect of significant job losses at Govan and Scotstoun doesn't even bear thinking about - it could tip our economy over the edge."
A spokesman for BAE Systems said they were working with the UK government to "agree a revised baseline" for the frigates.
The First Minister demanded that David Cameron deliver on his government's promises.
Sturgeon said: "Workers at the Clyde yards were given a clear promise by the Tory government and the Labour party that they would build the frigates and that their jobs would be protected.
"First the Tories cut the number of frigates; now we hear that they may delay or move the orders putting jobs at risk."
She added: "David Cameron must commit to delivering these contracts, and ensuring jobs are protected at BAE on the Clyde. Workers in the shipyards should be treated with respect for their skills and experience, not betrayed with empty promises.
"It would be an absolute betrayal if David Cameron was to go back on his promise now, and shows the folly of the Labour party for signing up to Tory promises.
"The SNP in government has worked closely with BAE and the trade unions to support the yard and we will give them our full support over the coming months to ensure that the promises that were made are delivered."
Scottish Labour leader Kezia Dugdale called out the Conservative government for "false promises".
Dugdale said: "It is completely unacceptable that workers on the Clyde are reading these reports in newspapers before they have been informed.
"If these reports are correct, workers on the Clyde will have been betrayed by a Tory government making false promises.
"Shipyard unions will have the full support of Scottish Labour in protecting these jobs.
"Clydeside shipbuilders are the best in the world and investment in the yards so that facilities match the skills of the workforce is essential to allow them to win future contracts."
The Labour leader added: "It is essential that the Type 26 project goes ahead as planned and as promised. Promises were made to workers on the Clyde, they must be kept."
Conservative leader Ruth Davidson said she had been assured the orders would go ahead as planned, as set out in the Strategic Defence and Security Review (SDSR).
Davidson said: "I spoke to the Secretary of State for Defence this morning to seek reassurances regarding orders to BAE systems on the Clyde.
"Michael Fallon confirmed that the orders for the Type 26 frigates and OPVs [Offshore Patrol Vessels] would go ahead as planned and as set out in the SDSR in November.
"It is important to monitor workforce issues at BAE between the winding down of work on the aircraft carriers and starting work on the Type 26 programme and I expect everyone - BAE, unions and government - to endeavour to make the transition between projects as smooth as possible and give the workforce the security they deserve."
The Lib Dems said the Clyde workforce needed assurances from the Prime Minister.
Party leader Willie Rennie said: "There are serious concerns about the future of the orders at the yard and it's important that the Conservative government gives an absolute commitment.
"They need to end the feast and famine of orders so the workforce can be maintained at a steady level."
