Firefighters at the Sellafield nuclear site will stage a fresh strike on Monday in a long running dispute over pay.
Members of the GMB union will walk out for 12 hours from 6am following strikes last year.
Sellafield said there will be emergency cover.
The dispute started last summer, with the union rejecting an offer it said was worth £4.30 a week.
GMB official Chris Jukes said: "We acknowledge Sellafield has made a new offer in December including an allowance related to security and terrorism, but it falls short of expectations and view expressed in negotiations.
"The two sides are not miles apart, but there needs to be further local negotiations to reach a settled position."
A Sellafield Ltd spokesman said: "As always, we will work with other agencies to try to minimise disruption for the public.
"Full emergency safety cover will be in place during this strike."