The risk of a strike increased after a special court on Friday rejected the employers organisation's filing that a work stoppage would be illegal.
The Industri Energi union issued a strike warning in a bid to obtain separate wage negotiations for drilling employees, apart from the negotiations
for other oil sector employees.
If the mediation currently underway fails, 159 employees working on two offshore platforms off Norway will stop work on Saturday at midnight (2200 GMT), Industri Energi said.
The strike would only affect drilling on the two installations and would not have an impact on Norway's oil production.
The country is Europe's biggest oil exporter and the world's eighth biggest.
The NHO employers' organisation said meanwhile it sees the stoppage as an extension of a 16-day strike earlier this summer.
The Norwegian government intervened to end that strike just minutes ahead of a threatened lockout, with the two sides ordered to binding arbitration the outcome of which is not yet known.