More than 2,500 workers at the giant Sellafield nuclear reprocessing plant in Cumbria are threatening industrial action over pay.
Management at Sellafield say industrial action should be avoided
The site's industrial workers want their shift rates brought into line with the company's white-collar employees.
Unions say plant owner British Nuclear Fuels Limited (BNFL) has broken a promise to equalise pay rates between staff and managers.
Unions have already voted to take industrial action if further negotiations fail.
They are looking to increase industrial workers' pay by around £2,000 a year.
BNFL says its existing shift rates are already amongst the highest in the UK.
Peter Kane, from the GMB union, said: "The difference between the bottom end of the staff side and ourselves is something like £2,000 in shift allowance.
"My people believe that anyone working weekends and night shifts should get the same pay.
"A night shift to me is worth the same as a night shift to a team leader."
A BNFL spokesman said: "BNFL believes that after all the progress made in the past three years, it is disappointing that industrial action is being mooted ahead of any final proposals or decisions, not least because we are still effectively a year ahead of any implementation date.
"The company is still committed to resolving this issue and believes that a solution can be found to equalising shift pay.
"BNFL believes that industrial action can and should be avoided.
"The company is prepared to review all of the options and believes that agreement can be achieved through negotiations."