The long-running dispute at the nuclear clean-up site is over requests for ‘Sellafield Specific Allowances’ bonus payments.

Workers demanding the extra payments include electricians, joiners, pipefitters, riggers, groundworkers, welders and painters.

Unite general secretary Sharon Graham said: “Sellafield employers seem intent on siphoning off the profits without paying our members a fair share. Our members are highly skilled and operate in an extremely challenging and hazardous environment. Despite this construction employers are refusing to pay an allowance for our members’ skills and dedication.

“Our members have the complete support of Unite in their dispute.”

Unite regional officer Ryan Armstrong added: “Strike action would inevitably result in work at Sellafield grinding to a halt but the employers have brought this dispute on themselves by refusing to negotiate.

“There is still time to avoid strike action but the employers must return to the table with a viable offer.”

The Unite ballot will start today and will conclude on Thursday 24 July.