Contract workers at the Sellafield nuclear site in Cumbria have begun unofficial industrial action in support of workers at a Lincolnshire oil refinery.
Workers at the Total refinery are mounting the unofficial strike action over the use of foreign workers.
They walked out last week in protest at the use of Italian and Portuguese labour which, they claim, is undercutting British workers.
It has already caused a series of sympathetic walkouts across Britain.
Workers at Heysham nuclear power station in Lancashire and Staythorpe power station near Newark in Nottinghamshire were among others taking unofficial action for the first time today.
Under EU law, companies in Britain can bring in workers from member countries.
But British union leaders claim companies are using an interpretation of recent European Court rulings illegally to exclude UK workers from even being considered for job vacancies.
Total denies it is discriminating against British workers.
One government minister says rulings by the European Court of Justice have undermined worker protection but British Prime Minister Gordon Brown has condemned the walkouts.
