Workers at the Phillips 66 oil refinery in South Humberside walked out unofficially for four days last week.
Up to 600 walked out over safety concerns following a gas leak the previous week which injured two men.
The refinery processes barrels of oil into petrol and diesel.
Mechanical engineers, scaffolders, welders and pipe-fitters are among the workers who walked out.
GMB union officer Shaune Clarkson said, “All we want is a reassurance that the site is safe and some safety issues addressed.”
On Friday of last week workers cast their vote by a show of hands, with many of those voting “no” at a mass meeting at the site to return to work.
One worker said of bosses, “They’re not going to do anything until someone is killed.”
Crane drivers called off a second day of planned strike action last Friday to consider a new pay offer.
HTC Plant tabled a proposal after the first strike by some 180 Ucatt union members.
Drivers were calling for an 8 percent increase.
HTC imposed a 3 percent pay increase after the offer had been decisively rejected by crane drivers.
Some 30 anti-blacklisting campaigners took part in a protest at the construction site for a new power station in Carrington, Greater Manchester.
Activists and two workers who say they have been blacklisted blocked the main entrance. Lorries were backed-up and no vehicles were let in. No workers crossed the picket line.
Campaigning is set to continue to get the blacklisted workers onto the Carrington site.
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