* Labour unions threaten strike from Sept. 30 onwards
* Conflict could cut Norway’s oil, gas output by 22%
* Mediation set for next week to try to avert strike (Adds detail, background)
OSLO, Sept 25 (Reuters) - Norwegian oil firms plan to close down 22% of the country’s oil and gas output, or 900,000 barrels of oil equivalent per day, if workers go on strike next week, the Norwegian Oil and Gas Association (NOG) said on Friday.
Some 324 out of 7,300 employees on offshore platforms plan to strike from Sept. 30 if annual pay negotiations with employers fail, trade unions Safe, Industri Energi and Lederne said on Wednesday.
If Norway’s state-appointed mediator is unable to broker a deal, union members will be eligible to go on strike and the dispute will escalate.
Norway pumps just over 4 million barrels of oil equivalent per day (boepd), half in the form of crude and other liquids and half from natural gas, making it a major global energy supplier.
Fields and platforms that could be forced to shut are Equinor’s Johan Sverdrup, Snorre B, Kvitebjoern, Aasta Hansteen, Kristin, Tyrihans and Valemon, the NOG said.
Wintershall Dea’s Maria field would also have to shut, it added.
At the Johan Sverdrup field, the largest oil-producing field in Western Europe, 88 workers from Safe and 43 from Lederne would strike, including some control-room operators, officials at the two unions said on Wednesday.
Sverdrup’s technical production capacity was increased to 470,000 barrels of oil per day (bpd) in April from an original 440,000 bpd.
The field’s output is currently capped, however, at 415,500 bpd as part of Norway’s agreement with OPEC and other producing nations to curb output until the end of 2020.
Several other facilities will also be affected by a strike, unions have said, but were not on NOG’s list of planned shutdowns.
Some 25 workers will strike at ConocoPhillips’s Ekofisk Lima platform, Safe said, while 39 service workers employed by ESS at Aker BP’s Ula and ConocoPhillips’s Eldfisk Bravo also plan to join.
Unions have not published details of their demands.
In 2012, the government invoked emergency powers to end a conflict after 16 days when employers threatened a lockout of workers that would have shut down Norway’s entire oil and gas output. (Writing by Terje Solsvik; editing by Gwladys Fouche and Barbara Lewis)