The dispute centres on the failure of Dounreay Site Restoration Limited (DSRL), a consortium owned by Cavendish Nuclear, CH2M and Aecom, to meet Prospect's claim for a 2.3% pay rise.

That claim, submitted in March 2017, was an attempt to arrest the erosion of wages Prospect members had been subject over a number of years. DSRL’s best offer was 1.75%, a further cut in members’ real wages.

“Our members at Dounreay and across the nuclear decommissioning estate are in effect working to make themselves redundant,” said Richard Hardy, Prospect national secretary for Scotland.

“Successful completion of their jobs means that work at the site will be hugely reduced. Therefore we think it’s only fair that those members don’t also see the value of their wages and pensions being cut at the same time," he said.

“We know that the owning companies are making money out of the decommissioning operation. We know that this is largely because of the hard work of our members and the innovations that they bring to their roles, despite them knowing that shortening a job means they are shortening their employment.

“Reducing real wages not only affects our members but the whole economy of the north. This is public money being used to fund massive payments to foreign-owned companies. We’ve said repeatedly that wealth created in Caithness shouldn’t be cashed in California,” said Hardy.

The GMB and Unite unions on site are also balloting their members. The ballot closes on 22 December, with action likely to take place on 15 January.