Contractors at Total's Lindsey refinery in Lincolnshire began a protest on Wednesday after a project to build a hydro desulphurisation unit was given to an Italian company.
Unions say the firm has excluded local workers from the contract and has shipped in workers from abroad instead.
They argue that it flies in the face of promises made by Prime Minister Gordon Brown in 2007 to provide 'British jobs for British workers'.
Around 1,000 angry demonstrators gathered at a car park opposite the oil terminal today for a union meeting.
The action also comes as Britain faces a rapid rise in unemployment with almost 2m people now jobless.
A recent opinion poll showed around half of British workers fear losing their jobs over the next year as the economy declines.
Total has said protests at the refinery, which can process 200,000 barrels of crude oil a day, had not affected production.
The French company also said there would not be any lay-offs to the existing contractors as a result of the contract award.
However, the dispute began to spread today as workers at other sites staged unofficial strikes in support.
Hundreds walked out at the Grangemouth oil refinery in Scotland run by Ineos, around 300 workers demonstrated at a chemical plant in Teeside, and 50 workers protested at the Aberthaw power station in south Wales.
Ineos said production at Grangemouth was unaffected.
Derek Simpson, General Secretary of the Unite union, told BBC radio: 'It's not the question of foreign workers. It is the question that some of these companies ... are saying they will exclusively debar UK workers, they will not consider UK workers under any circumstances.'
He called on Gordon Brown to stop what he said could be illegal action by firms under European law.
Mr Simpson said there were plans for a national lobby of parliament by energy and construction workers, echoing protests across Europe.
More than a million demonstrators went on strike in France yesterday, calling for protection for jobs.
