Hundreds of workers across England and Wales have walked out in support of nearly 650 construction contractors sacked from the Lindsey Oil Refinery.
It came after about 1,200 workers staged unofficial walkouts at the North Lincolnshire plant, in a jobs dispute. Workers in Teesside, South Wales, Cheshire and Yorkshire are among those to have come out in support.
Expected talks aimed at resolving the dispute at Lindsey - owned by Total - have failed to go ahead, Acas has said. The sacked Lindsey workers have been told they have until 1700 BST on Monday to reapply for their jobs.
They had been building an additional plant next to the existing site in Killingholme, but withdrew their labour last week in protest at a sub-contractor axing 51 jobs while another employer on the site was hiring people. The workers argued this broke an agreement not to cut jobs while there were vacancies elsewhere on the site. Total insists no such agreement was in place.
Workers insist the assurances were given in February following a bitter dispute in which they said foreign labour was being used to exclude British contractors and to undermine hard-won conditions.
What became known as the 'foreign workers row' led to to a wave of unofficial strikes and protests at refineries and power stations across the UK. Workers are now claiming management at the Lindsey refinery are using the redundancy process to victimise activists involved in the previous wildcat strikes.
Meanwhile, workers at a number of sites have walked out in support of those who have lost their jobs in North Lincolnshire:
In Teesside, some 1,100 construction workers on a new biofuel plant project, owned by Ensus, walked out. A company spokesman at the site - on the Wilton chemical complex - said the action was not taken by people directly employed by them
About 300 contract workers downed tools at Aberthaw power station in south Wales, with some holding a peaceful protest outside. The company said no RWE npower staff were involved and operations were not affected
Up to 450 contract maintenance staff walked out at the Stanlow Oil Refinery in Ellesmere Port, Cheshire. Shell says the action will not affect production but may delay routine maintenance projects
Some contract workers have downed tools at Ferrybridge power station in West Yorkshire. Scottish and Southern Electric say the plant is operating normally
In North Yorkshire, contract workers took support action at Drax and Eggborough power stations, near Selby. The GMB union says the total number taking part at Drax, Eggborough and Ferrybridge is about 600 workers.
At Staythorpe power station near Newark, Nottinghamshire, 100 scaffolding contractors walked out unofficially for a second day
Workers at Fiddler's Ferry power station in Cheshire, owned by Scottish and Southern Energy, also showed their support by walking out.
Text messages were reportedly being sent to fellow workers around the UK to encourage them to take action.
One of the sacked Lindsey workers said: "We are asking for support from workers across the country which I am sure will be given. Total will soon realise they have unleashed a monster.
"It is disgraceful that this has happened without any consultation."
Another sacked contract worker, John McEwan, said: "We were left no option. If we have to defend the rights of our men on these sites and our pay and conditions then we have to do that."