Decommissioning at a nuclear site in Caithness looks set to be disrupted after union members among the workforce voted to strike next Wednesday.
UKAEA said safety at the site would not be affected by strike action
They are in dispute with operators, the UK Atomic Energy Authority (UKAEA), over the current year's pay claim.
Almost 87% of GMB members have backed industrial action and 90% supported an overtime ban at Dounreay.
UKAEA said it hoped an agreement would be brokered to avoid the need for strike action.
The GMB's national officer Mick Rix said feelings were running high about what he said was the authority's failure to make a pay offer.
Previous ballots by two other unions have also shown a substantial majority in favour of industrial action.
UKAEA said long-standing arrangements were in place at Dounreay to ensure safety would not be compromised at the former fast reactor complex if a strike were to take place.