Hundreds of workers in walk-out at Dounreay
More than 500 workers at the Dounreay nuclear power site have gone on strike in a pay dispute.
Members of Unite and GMB unions have walked out after rejecting a revised offer from Nuclear Restoration Services (NRS).
The Prospect union said its members had voted to accept the deal.
Unite and GMB members plan to hold two weeks of working to rule and no overtime. Another day of strike action is planned for 29 May.
About 200 workers have been on a picket line outside the site.
The revised offer proposed a one-off £500 payment on top of a basic 4.5% increase.
NRS said it was committed to finding a "fair and affordable" resolution.
Unite said the offer amounted to a substantial pay cut as inflation - in terms of the retail prices index - stood at 11.4% when the pay increase was due in April 2023.
Dounreay on the north Caithness coast near Thurso dates to the 1950s and was the site of Scotland's first operational nuclear reactor - the Dounreay Materials Test Reactor - which achieved criticality in 1958.
The complex is now being decommissioned.