More than 1,300 offshore workers are to stage a 48-hour strike in a dispute over pay.
Unite warned that dozens of oil and gas platforms will be brought to a “standstill” by the walkout from 24 April.
The union has previously warned of a “tsunami” of industrial unrest in the offshore sector over pay and conditions.
Unite's general secretary Sharon Graham said: “Oil and gas companies in the offshore sector are enjoying record windfall profits.
“There’s no question that contractors and operators can easily afford to give members a decent pay rise.
“The scale of corporate greed in the offshore sector has to be challenged.
“1,350 offshore workers will now take part in an unprecedented tsunami of industrial action over 48 hours with hundreds more set to join them.
“Unite will support all our members every step of the way in this fight for better jobs, pay and conditions.”
Workers taking industrial action include electrical, production and mechanical technicians in addition to deck crew, scaffolders crane operators, pipe fitters, platers and riggers.
Unite industrial officer John Boland added: “This is not exclusively about pay but also working rotas, holidays, and offshore safety.
“The workforce has been taken for granted for years but now their value will be acutely felt when strike action will bring dozens of platforms to a standstill.”
Meanwhile, the Royal Navy could see delivery of its Type 31 frigates significantly delayed, as workers at a Scottish yard are poised to down tools for weeks in their battle for higher pay.
Around 100 workers at the Rosyth yard employed by contractor Kaefer are set to strike after overwhelmingly supporting industrial action.
Bob MacGregor, Unite's regional industrial officer, warned workers were “prepared to take 12 weeks all-out strike action to get a decent wage rise”.
The union claimed it would threaten progress on the £1.25bn frigate contract at the Babcock-owned yard in Fife.
Some 98.4% of workers backed strike action, the union said on Friday.
After they announced their plans to strike, workers were offered a below inflation pay rise of 7.2%, which Unite said had been rejected by workers.
MacGregor said “Kaefer just simply doesn’t get it” and claimed that “the company first refused to make any offer for months, and then they panicked following the strike vote”, adding: “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.”
The Royal Navy has ordered five Type 31 frigates, which are known as the Inspiration class.
HMS Venturer is the first set to be built, followed by Active, Formidable, Bulldog and Campbeltown.
When delivered, the 139 metre long vessels will carry 107 crew.
The workers set to strike include painters, cleaners, scaffolders and support service strike, and the union said they will down tools between 17 April and 10 July.
A Babcock spokesman said: “We are aware of the situation between Kaefer and their 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.”
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