UPDATE 6-Equinor maintains oil output as more workers prepare to strike

* Workers strike at Johan Sverdrup field, western Europe’s largest

* Equinor continues production at the 470,000 bpd field

* Lederne union to escalate strike from Oct. 4

* 126 workers to stop working at four offshore fields (Recasts after statement on strike escalation)

OSLO, Sept 30 (Reuters) - Norway’s Lederne labour union will escalate offshore industrial action to four additional fields, it said on Wednesday after dozens of workers went on strike at the Johan Sverdrup oilfield, western Europe’s largest.

Sverdrup operator Equinor said it could maintain safe operations despite the strike by 43 workers at the 470,000 barrels per day (bpd) field, which accounts for close to a quarter of Norway’s oil output.

Lederne said that strike will be escalated from Oct. 4, with a further 126 union members halting work at the Equinor-operated Gudrun, Gina Krog and Kvitebjoern fields as well as Neptune Energy-operated Gjoea.

“We believe that those four new fields will have to shut production because of the strike,” Lederne union chief Audun Ingvartsen told Reuters, adding that all workers at the Gjoea platform were members of Lederne.

Workers went on strike after wage talks failed between the union and the Norwegian Oil and Gas Association (NOG), which represents oil and gas companies.

The association said it regretted the strike escalation, which would have “severe negative impacts” for an industry facing an already challenging situation.

The Gudrun, Gina Krog, Kvitebjoern and Gjoea fields produced a total of 260,000 barrels of oil equivalents per day in July, the latest available data from the Norwegian Petroleum Directorate shows.

Two other, larger offshore unions, Industri Energi and Safe, have agreed to new wage deals and will not strike.

Equinor’s spokesman said the company was still assessing the potential impact from the proposed strike escalation.

Lederne’s Ingvartsen said the union called Norway’s petroleum safety watchdog to investigate whether it was safe to operate Svedrup with fewer staff.

The union negotiated on behalf of about 1,000 offshore oil workers, according to Norway’s government-appointed wage mediator.

The NOG said Lederne had demanded a larger pay rise for its members than the two other unions.

Lederne has disputed that claim and said that companies had been unwilling to adjust contracts to reflect changes in work practices, adding that this would not cost more.

Under Norwegian rules, the union must give a four-day warning before additional workers can join the strike.

Norway pumps a little more than 4 million barrels of oil equivalent per day, half in the form of crude and other liquids and half from natural gas. (Editing by Elaine Hardcastle, Jason Neely and David Goodman)