Almost 35,000 private-sector workers organised by Norway's largest labour unions plan to go on strike from April 8 unless a deal is found over wages, pensions and other compensation, the unions said on Tuesday.
The first wave of a strike would hit large parts of Norway's metals production by leaving smelters idle, and would have significant impact on the output of fertilisers. But the output of oil and gas from western Europe's largest producer would initially be spared, the unions said.
Norway's Norsk Hydro is a major producer of aluminium, while Yara is among the world's largest makers of fertilisers.
Other companies that would be hit include offshore engineering companies Aker Solutions and Kvaerner .
Starting on Wednesday, a state mediator will attempt to broker a deal ahead of an April 7 deadline.
In case of a protracted conflict, the Norwegian Confederation of Trade Unions, known under its LO acronym, and the smaller Confederation of Vocational Unions (YS) could later escalate a strike to include more than 200,000 people.
Reporting by Terje Solsvik