Royal Navy frigates could see "significant delays" as yard workers at Rosyth prepare to strike in a dispute over pay, union bosses have warned.
Unite said about 100 workers at the Fife yard employed by contractor Kaefer support industrial action.
The union said workers were prepared to strike for 12 weeks to "get a decent wage rise".
It claimed it would threaten progress on the £1.25billion frigate contract at the Babcock-owned yard.
About 98.4% of workers backed strike action. These include painters, cleaners, scaffolders and support service strike.
Unite said they would down tools between April 17 and July 10.
Offer
After they announced plans to strike, staff were offered a below-inflation pay rise of 7.2%, which was rejected.
Unite's regional industrial officer Bob MacGregor claimed the company refused to make any offer for months, then "panicked following the strike vote".
He told the BBC: "Kaefer, in turn, are blaming Babcock who own the yard for this situation but it's a mess they have jointly created.
"It's a really shoddy way of managing industrial relations at Rosyth.
"The imminent strike action will have a knock-on effect for the Type 31 contract, and it will undoubtedly lead to significant delays."
Babcock was awarded the frigate contract after a competition between rival consortia.
Five frigates ordered
The Royal Navy has ordered five Type 31 frigates, which are known as the Inspiration class. The vessels will carry 107 crew.
HMS Venturer is the first being built, followed by Active, Formidable, Bulldog and Campbeltown.
A Babcock spokesman said: "We are aware of the situation between Kaefer and its Unite members and will work with our sub-contractor to mitigate any impacts to our Rosyth operations."
A spokesman for Kaefer said: "We continue to support constructive dialogue between Unite and Kaefer to reach a mutually-acceptable resolution.
"The safety of our teams remains paramount and will not be affected by any potential industrial action."