Norway’s giant Johan Sverdrup offshore oilfield faces a potential shutdown as talks open between a workers union and the Norwegian Oil & Gas Association (Norog) to try to head off a strike that could also impact a clutch of other fields.

A dozen workers that are members of the Safe union are threatening to down tools at the Mongstad terminal from midnight on Monday if talks with the industry body aimed at breaking an impasse over a 2020 wage settlement with Equinor fail.

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John Sverdrup operator Equinor warned that, it mediation is not successful, the potential strike could reduce crude storage and harbour capacity at Mongstad. This could in turn affect production at Sverdrup and the Troll field, among others, “and it could be necessary to shut down production there until further notice”.

Other fields that could be impacted include Kvitebjorn, Visund, Byrding, Fram and Valemon, with gas output exports from the Troll area also in danger of being hit.

The Safe union, in a statement issued in Norwegian, said: “ At a time when Equinor has wasted hundreds of billions of kroner in foreign investment, the company has shown little willingness to value the employees in Norway that creates the company's financial results.”

The foreign investments claim relates to Equinor’s huge writedowns on its US onshore assets. The company last week announced an asset sale that is seeing it quit the Bakken shale play.