"Knarr's production has been stopped because of the strike," company spokeswoman Kitty Eide told AFP, adding that the field's output is around 23,000 barrels per day.
The shutdown was prompted by around 100 people at Knarr going on strike as part of a wider stoppage by nearly 670 people working on nine platforms or ships in the region.
They are members of the Safe union and striking over wages and pensions.
Employers association Rederiforbundet said that unions had now also issued a strike call to 900 additional staff who could take action at the weekend, potentially affecting another 20 sites.
That strike could have "huge consequences for the reputation, the economy and employment" in the oil sector, warned Jakob Korsgaard, who is negotiating on behalf of bosses.
The Norwegian strikes are adding to supply worries that have pushed the oil price higher in recent weeks.
In addition to Washington's efforts to stop anyone from buying Iranian oil, production outages in Libya, Venezuela and Canada have also been causing the global crude market headaches.
For now, however, the impact of the stoppages on Norway's overall oil production is limited.
The Nordic country, Europe's biggest oil producer, last year clocked up an average output of nearly 1.6 million barrels per day.