Lindsey oil refinery workers are protesting over job cuts
An unofficial strike at a North Lincolnshire oil refinery is continuing for a fifth day, and has spread to other sites in Britain.
About 1,200 contractors at the Lindsey refinery have walked out.
Contractors at Cheshire's Fiddlers Ferry Power Station and Aberthaw in south Wales downed tools in sympathy.
The Lindsey workers withdrew their labour last week in protest at a sub-contractor axing 51 jobs while another employer on the site was hiring people.
Meurig Thomas, a shop steward representing the Unite union at Aberthaw, said between 200 and 300 contractors at the power station, west of Cardiff, had walked out in sympathy with workers at the Lindsey oil refinery.
They were expected to return to work on Thursday, but may down tools again if the row was not resolved, he added.
Up to 140 contractors are also striking for a third day at Fiddlers Ferry Power Station in Widnes, Cheshire.
David Porter, director of AE&E Lentjes, contractors at Fiddlers Ferry, said workers had taken unofficial action since midday on Monday in support of the Lindsey oil workers.
"What happens after today, I don't know. I guess they will be taking their lead from the Lindsey oil talks," he told the BBC.
Planned talks between unions and Lindsey refinery owner Total aimed at breaking the deadlock stalled on Tuesday.
Total said the strike was illegal and talks could not begin until employees returned to work.
The GMB union has called for the employers to meet with them and the conciliation service, Acas.
Last month, Aberthaw workers downed tools in a dispute over the hiring of local labour.