Main contractor Alstom is building stations at Staythorpe in Nottinghamshire for RWE and at the Isle of Grain in Kent for EON.
Unions claim that they plan to use 250 Polish workers to build the next phase of Staythorpe and that the firm is barring the employment of any UK workers.
Alstom strongly denies that allegation.
The unions plan to demonstrate outside the sites on Wednesday 7 February from 7am.
Keith Hazelwood, GMB national secretary siad: "Following the dispute at the Lindsey Oil Refinery, the trade unions are pleased that our engineering construction members' grievances are finally being recognised."
"There is still some way to go but at least people are beginning to understand what we have been saying. We now plan to follow this up with a series of meetings and demonstrations to get action to stop UK workers being denied work on UK projects."
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