Lindsey oil refinery workers are protesting over job cuts
Unofficial strikes at oil terminals and power stations have spread to more sites across the UK.
Some 1,200 contract staff walked out in a row over jobs at Total's Lindsey oil refinery in North Lincs last week.
The action has spread to power stations at Drax and Eggborough in Yorkshire and Ratcliffe in Nottinghamshire, and BP's Saltend refinery near Hull.
Workers are also out at the BOC oxygen plant at Scunthorpe, in addition to two other strikes begun earlier this week.
Action started at power stations at Fiddlers Ferry in Cheshire on Monday and Aberthaw in south Wales on Wednesday.
The Unite union said conciliation service Acas was dealing with both parties in the dispute but that there were no direct talks between the two sides.
The Lindsey workers withdrew their labour in protest at a sub-contractor axing 51 jobs while another employer on the site was hiring people.
Planned talks between unions and employers aimed at breaking the deadlock stalled on Tuesday.
Total said the strike was illegal and talks could not begin until workers returned to their jobs.
The Lindsey refinery suffered strikes earlier this year over the employment of non-UK workers.