The dispute over jobs on a scheme to build an oil refinery in Lincolnshire has turned ugly after hundreds of protesting workers were sacked.
Site owner Total has written to 900 workers at the Lindsey refinery site informing them they had until Monday to reapply for their jobs.
The move has sparked sympathy strikes at sites across the country.
Activists have also warned that power workers could potentially also join the protest, threatening electricity supplies.
Local reports said contract workers at the Staythorpe power station in Nottinghamshire and Ferrybridge power station in Yorkshire had walked out early this morning after hearing about the sackings.
Workers at sites including Ratcliffe in Nottinghamshire, Didcot in Oxfordshire and Aberthaw in South Wales had also joined the wildcat action in recent days in sympathy over the Lidsey situation.
The dispute arose when one contract laid off more than 50 workers while another was employing people for the job. The site had been the centre of unofficial strikes earlier this year over anger at foreign labour numbers.