More than 500 nuclear power station workers will walk out this week amid a row over pay.
Unite union members at the Dounreay plant in the Scottish Highlands plan to take 24-hour strike action on Wednesday after rejecting a revised pay offer from their employer Nuclear Restoration Services (NRS).
The union members will also support an overtime ban from Thursday.
NRS proposed a one-off £500 payment on top of a basic 4.5% increase.
Unite said 80% of the 92% turnout rejected the deal, with the union saying it represented a “significant real terms pay cut” as inflation – in terms of the retail price index – stood at 11.4% when the pay increase was due in April 2023.
A further day of industrial action has been scheduled for 29 May, with Unite saying it is prepared to add additional strikes if “no movement is made by NRS”.
NRS said it was “disappointed” in the decision but remains “committed to finding a resolution that is fair and reasonable”.
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The Unite workers include craft technicians, general operators, chemical and electrical engineers, maintenance fitters and safety advisers.
Unite has claimed the remuneration package of the highest-paid NRS director went up from £331,000 to £651,000 at March 2023, and the company paid dividends of £2.1m in the same period.
Marc Jackson, Unite industrial officer, said offers amounting to a “significant pay cut” would not be tolerated.
He added: “We have a growing membership at Dounreay, which is down to the hard work of our shop stewards, and NRS need to realise, if they don’t already, that we are heading for prolonged industrial action.
“Unite is actively looking at further days of action because NRS seem incapable of resolving this dispute through negotiation.
“The company should be under no illusions as to the determination of our members to get the pay rise they deserve.”
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It is understood union workers represented by Prospect will accept the offer, while GMB members will back strike action.
Lesley-Anne MacAskill, organiser at GMB, said the civil service pay remit, which is a set of pay guidelines, had been used as an excuse to delay engaging with workers on pay.
She has now written to Andrew Bowie MP, minister for nuclear and renewables, urging him to remove NRS from a civil service pay framework.
In her letter, Ms MacAskill said: “Our members have been left to endure a cost of living crisis for well over a year without the support of a deserved and overdue pay rise.
“This strike would have been entirely avoidable if you, as an employer, had removed Dounreay from the civil service pay remit.”
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In response to Unite’s strike action, a spokesperson for NRS said: “We are disappointed by today’s announcement but remain committed to finding a resolution that is fair and affordable.
“Our contingency plans are being implemented to ensure the site remains safe, secure and compliant during any period of industrial action.”