Nicola Sturgeon has challenged the Prime Minister over unions raising fears of job losses on the Clyde if the Government pulls back from orders to build frigates.
The SNP leader and First Minister said it would be an “absolute betrayal” if David Cameron “went back on his promise” to workers.
But Scottish 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).
It comes after unions spoke of worries over job cuts at defence giant BAE Systems on Friday.
Gary Smith, GMB Scotland secretary, said: “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.”
Mr Smith vowed to “resist any redundancies or withdrawal of work” by using “every tool we have at our disposal”.
On Saturday, Ms 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.
“The promises made to the workers at the Clyde yards must be met. David Cameron must commit to delivering these contracts, and ensuring jobs are protected at BAE on the Clyde.”
She said the SNP in government has worked closely with BAE and the trade unions and would give them “full support” over the coming months.
Ms Davidson said she spoke to the Defence Secretary on Saturday 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,” she said.
“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.”
Scottish Labour leader Kezia Dugdale said shipyard unions would have her party’s full support in protecting 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,” she said.
“It is essential that the Type 26 project goes ahead as planned and as promised.”
A BAE Systems spokesman said: “Following the SDSR, we are working with the Ministry of Defence to agree a revised baseline for the Type 26 ships and a production schedule for the two additional Offshore Patrol Vessels in Glasgow.
“We are engaging our trade unions as we work through this process. Our focus is to deliver the capability the Royal Navy needs, while ensuring the best value for UK taxpayers.”