Contract workers at the Sellafield nuclear site joined the wildcat strikes over foreign labour despite calls from the Government for the industrial action to stop.
The stoppage at the Cumbrian site is expected to be followed by a series of walkouts across the country in the escalating row over the hiring of Italian and Portuguese workers on a power station project.
The atrocious weather could affect the number of workers joining the action, but union sources said they expected widespread action as feelings were running high.
Around 700 contractors at the Grangemouth oil refinery in central Scotland, who took unofficial action on Friday, walked out again.
However they also decided they would return to work on Tuesday. The action at the plant near Falkirk followed a mass meeting of staff, one of several taking place at various sites across Scotland.
Business Secretary Lord Mandelson maintained that UK firms and workers were not being discriminated against and called for the unofficial strikes to stop.
Contractors at the Heysham nuclear power station in Lancashire are also expected to decide whether to join the unofficial walk-outs in support of workers at the Total oil refinery in Lincolnshire, where the dispute started.
Bosses from Total will meet with sub contractors and union leaders for hastily-arranged talks in Scunthorpe.
Lord Mandelson said he understood the concerns of British workers, but he stressed that Total, which runs the Lincolnshire power station at the centre of the row, had refuted claims that UK workers had been excluded from contracts. "I hope in the light of that people will be reassured and call off these unofficial disputes," he told BBC TV.
Management at Sellafield said the contractors who walked out were building new storage facilities at the site.
