Staff at Cape Industrial Services Limited, at the Fellside CHP Plant, are preparing to launch the 24-hour action as part of a long-running dispute over terms and conditions.
The Unite union represents 19 workers at the firm, which is based outside the Sellafield site.
The workers, including scaffolders, thermal insulation engineers and labourers have been operating a continuous overtime and work to rule since January 3.
Their dispute is over workers attaining improved terms and conditions set out by the National Agreement for the Engineering and Construction Industry (NAECI).
Unite says its members first raised concerns with Cape management last May.
A Sellafield Ltd spokeswoman said: “We have taken steps to ensure that safety and security at the site will be unaffected.”
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