Spglobal - Norway's oil and gas industry is assessing the likely impact of a decision by an offshore managers' union to step up a strike already thought to have cut output by as much as 330,000 b/d of oil equivalent.

The Lederne union, one of the industry's smallest trade unions, said overnight that it would extend its strike on Oct. 11 to include two platforms at the flagship Ekofisk field as well as two satellite fields that feed the Oseberg crude stream, and Kristin, a satellite of the Asgard crude stream. Ekofisk is operated by US upstream company ConocoPhillips, with crude loading at Teesside in the UK, while Oseberg and Kristin are operated by state-controlled Equinor.

Industry group Norwegian Oil & Gas, which is responsible for pay negotiations on behalf of oil and gas operators, told S&P Global Platts that it was not yet sure of the impact on production and no formal negotiations were underway with the union. Equinor said it expected an assessment of the impact to be released in due course, while ConocoPhillips did not respond to a request for comment.

Equinor has maintained production at its flagship Johan Sverdrup field despite a walk-out by 43 Lederne members at that facility, prompting claims by the union that employment rules are being flouted, while six other fields have been shut down since Oct. 6, with an estimated impact on Norwegian oil and gas output of around 8%.

Lederne has said its dispute is not only about pay, but industry moves to reduce the offshore workforce as technology enables some functions to be carried out from control centers onshore.

Norway is Western Europe's largest oil and gas producer, with oil output of about 2 million b/d, or around two-thirds of oil production in the wider North Sea region.