Workers at the Sellafield nuclear site will strike over two separate disputes relating to pay and health and safety.
The GMB union said 400 of its members working as health physics monitors will strike for four hours from 8.30am tomorrow and then again for 48 hours from 6.30am on Wednesday due to a dispute over pay re-grading.
The workers staged a 24 hour strike last month over the same issue and senior organiser Chris Jukes accused managers of "repeatedly moving the goalposts" when a "perfectly reasonable" deal was possible.
The Unite union said its members working for nine sub-contractors will strike for two and a half hours on September 1, 9 and 16 followed by a 24 hour walkout on the 23rd as part of a campaign to get a full-time union convenor instated at the site.
Regional secretary Mick Whitley said: "Unite has repeatedly called for meaningful talks, but they have been rebuffed at every stage, and our members have no alternative but to take industrial action.
"The continuing attitude of the bosses underlines the draconian attitude of the contractors at Sellafield and means that industrial relations are now teetering on the edge of the abyss."
In statement responding to the pay row Sellafield said: "This dispute centres on a fundamental difference of understanding about an agreement to reward a number of health physics monitors who carry out specific tasks in specific plants. Fairness is the key principle.
"That some of those individuals are entitled to further reward is not in dispute - the contention lies in the fact that we have always said that there must be criteria as to who does and does not qualify for the payment, and the GMB's desire for us to apply a blanket payment across the majority of the HPM workforce.
"We have worked hard through months of consultation and negotiation with the GMB to find a resolution, and they continue to decline our offer to involve (mediation service) Acas."