Workers are angry at the use of foreign labour
About 1,300 contract workers at the Sellafield nuclear site in Cumbria have walked out in a protest at the employment of foreign workers.
The action followed a meeting of mechanical contractors in one of the plant's car parks early on Monday.
Their action is in support of staff at the Lindsey oil refinery in Lincolnshire, who walked out last week over the employment of Italian workers.
A Sellafield spokesman said the action would not affect safety.
One of the strikers, GMB convener Willie Doggert, said: "All we want is a level playing field, it's not just about foreign workers, we need jobs to be advertised with transparency so that everybody gets a far crack of the whip at getting them.
"The jobs down the country were given to foreign workers without giving Great British workers the chance to bid for them.
"This has nothing to do with stopping people coming here, it's just about greater transparency."
The contractors on strike include scaffolders, riggers, pipe fitters and labourers working on building projects around the Sellafield site.
A spokesman for Sellafield Ltd said: "This meeting involves contractors working for companies operating under the National Agreement for the Engineering Construction Industry (NAECI), not Sellafield Ltd employees.
"Safety is paramount at Sellafield, and Sellafield Ltd is confident that any industrial action would have no impact on safety, security or production."
The industrial action is scheduled to last for 24 hours and contractors will reconvene on Tuesday to reassess the situation.