The walkouts began in Lincolnshire and spread to many other parts of the UK
Ministers are closely monitoring talks aimed at ending strikes at energy plants, the government says.
Hundreds of employees across the UK have walked out in support of striking workers in Lincolnshire who are angry at the use of foreign labour.
The Acas mediation service was talking to unions and employers on Saturday, as pressure grew on the government to act.
While no formal ministerial talks are planned, staff from several departments are in touch with energy firms.
Officials from Downing Street, the Business and Enterprise, and Energy and Climate Change departments are involved.
The original strike began at Lindsey Oil Refinery after owner Total gave a £200m contract to Italian firm IREM and prompted "sympathy strikes" across the country.
British Nuclear Fuels has also confirmed that 900 contractors at Sellafield station in Cumbria are to meet on Monday to discuss possible industrial action.
ENERGY WORKERS' PROTESTS
1. Grangemouth oil refinery, Central Scotland
2. Scottish Power's Longannet power station, Fife
3. Scottish Power's Cockenzie power station, East Lothian
4. Shell gas processing plant, St Fergus, Aberdeenshire
5. British Energy power station, Torness, East Lothian
6. Mossmorran chemical plant, Fife
7. Npower Aberthaw power station, south Wales
8. South Hook natural gas terminal, Milton Haven, Pembrokeshire
9. ICI chemical refinery at Wilton, Teesside
10. Corus steel plant near Redcar, Teesside
11. Scottish & Southern's Fiddler's Ferry power station, Cheshire
12. AES Kilroot power station, County Antrim
13. Marchwood power station, Hampshire
The government called in Acas to look into claims that British workers were being illegally excluded from engineering and construction projects, while unions have urged Prime Minister Gordon Brown to meet heads of industry in the sectors.
Labour backbencher John Cruddas said the government should be "banging heads together" to urgently address the underlying causes of the resentment.
He told the BBC: "It's the employers in these instances which are culpable and we need to confront some of them who are notorious in this sector."
Total has said there would be no "direct redundancies" as a result of handing the contract to construct a new unit at the Lindsey plant to the Italian firm, and that the tendering process had been "fair".
IREM employs a specialist workforce and its 300 or more employees would be paid the same as existing contractors on the project, Total's bosses added.
Cleethorpes MP Shona McIsaac (Labour) said the decision to hire foreign workers was like a "red rag to a bull" to local unemployed people.
But the Prime Minister's spokesman said the contracts were awarded some time ago when there was a shortage of labour in the construction sector.
Mr Brown said he "understood" people's worries and that the government was doing everything it could help individuals back into work.
Workers have demanded he fulfil a promise he made at the 2007 Labour Party conference of providing "British jobs for British workers".
However, employment Minister Pat McFadden said this had not meant that UK firms would be encouraged to flout European laws on free mobility of labour.
And UKIP leader Nigel Farage said Acas would be powerless to help because European law barred countries from reserving jobs for its own workers.
"It doesn't matter how many meetings are held, how much or how loud anyone shouts... we signed away our rights when we joined this prison of nations that is the EU," he said.
HAVE YOUR SAY
Where is the humanity in ruining someone's local environment by building a massive industrial refinery and then bringing in people from around the world to work there?
Ben Platt, Liverpool
TUC general secretary Brendan Barber said refinery workers were "rightly angry" at employers denying British-based workers the chance to apply for new jobs.
"The employer will be in breach of the law if they restrict any future vacancies to workers of a particular nationality or location," he added.
In a statement, Total said it "recognised" the concerns of contractors, that it had been a major local employer for 40 years and had 550 permanent staff employed at the refinery.
A majority of between 200 and 1,000 contractors working at the refinery were employed by UK firms, it added.
It said the affected unit was separate to the main refinery and that the action has not affected normal operations.