OSLO - Norway's petroleum output could be reduced if workers go on strike on Sunday, the Norwegian Oil and Gas Association (NOG) said on Friday.

Some 845 workers out of roughly 7,500 employees on offshore platforms plan to strike from June 12 if annual pay negotiations with employers fail, trade unions Safe, Industri Energi and Lederne have said.

If Norway's state-appointed mediator is unable to broker a deal, union members will be eligible to go on strike and the dispute could escalate the following week as more workers may join the strike.

Unions leaders have said that while oil production would likely be hit by any strike action, workers would initially seek to protect gas output due to the tight supply and high prices in Europe.

Any decision on shutdowns is ultimately up to the companies operating each field, however.

(Reporting by Nerijus Adomaitis, writing by Terje Solsvik, editing by Gwladys Fouche)