The move involves 1,500 construction workers across 34 contractors across disciplines including electricians, joiners, pipe-fitters, riggers, welders, groundworkers and painters.

A recent ballot returned a decisive mandate with well over 90 per cent support for strike and non-strike action.

Unite said employers have refused to pay Sellafield-specific allowances similar to other nuclear projects like Hinkley Point C and Sizewell C

A work-to-rule will see vital clean-up programmes and infrastructure maintenance face disruption.

Unite Regional Officer Ryan Armstrong said: “This action will inevitably result in work at Sellafield being delayed – but employers forced our hand by refusing to agree to our reasonable demand to other similar sites. They need to focus on coming up with a viable offer to avoid further escalation.”