A total of 3,000 GMB members working at Sellafield, in Cumbria, will go on strike tomorrow.
The 24-hour strike will take place from 6.01am on Wednesday 27 September to 5.59am on Thursday 28 September.
Picketing will take place at the site’s North Gate, Main Gate and Calder Gate from the start of strike and throughout the day.
It was announced on Monday 4 September that 76% of members voted to take industrial action.
This followed the company's decision to impose a below-inflation pay offer of 1.5%. RPI inflation is currently 3.9%.
Unite the Union is also balloting its 2,000 members with the result due on Monday 2 October.
Last year GMB members accepted a 0.25% pay rise in order to stop management cutting the pay of apprentices at the site.
Pay over recent years has failed to keep up with inflation and from next year the majority of Sellafield workers will have to pay more towards their pensions.
GMB says minimum safety manning levels will be maintained so that the workforce and community are safe: