About 755 Norwegian workers on seven oil and gas fields could go on strike from Saturday, hitting output from western Europe's top producer, if a new wage deal is not agreed before a Friday deadline, trade unions said on Monday.
A final round of mandatory talks will be hosted by a state mediator on June 30 and July 1 in an effort to avoid disruption that could start the following day.
The affected fields account for nearly 18 percent of Norway's oil output and a little more than 17 percent of its natural gas, Reuters calculations show.
Combined oil output was about 285,000 barrels per day in the first four months of the year, with natural gas output at 48.5 million cubic metres (mcm) per day.
Norway currently produces about 1.6 million barrels of crude and 280 million standard cubic metres of natural gas per day. Its combined natural gas liquids (NGL) and condensate output is about 400,000 barrels.
Employers have argued that a plunge in oil prices since 2014 must be accompanied by cost cuts and flexible work practices to help to keep the industry competitive.
Unions, meanwhile, say that members should receive pay increases matching those in other industries.
The Industri Energi union said it would take out 524 members if the talks break down, affecting the Statoil-operated Oseberg, Gullfaks and Kvitebjoern fields.
The SAFE union said it would take out 156 workers on ExxonMobil's Balder, Jotun and Ringhorne fields.
In addition, 75 workers on Engie's Gjoea field would also go on strike, the smaller Lederne union said.
Engie said it would shut Gjoea in the event of a strike, while ExxonMobil said
a strike would affect its operations.
Statoil declined to comment.
A protracted conflict could ultimately result in more than 7,400 workers going on strike, data from the state mediator's office showed.
"We do, of course, wish for mediation to lead to a deal, so that conflict is avoided," SAFE said in a statement.
The three labour unions will negotiate on behalf of the oil workers, while Norwegian Oil and Gas (NOG) will represent the companies.
In 2012 a 16-day strike among some of Norway's oil workers cut the country's output of crude by about 13 percent and its natural gas production
by about 4 percent.
(By Stine Jacobsen and Terje Solsvik; Additional reporting by Nerijus Adomaitis and Henrik Stolen; Editing by Louise Heavens, David Goodman and David Evans)