Norwegian oil and gas workers have walked off the job amid concerns about Europe's gas supplies.
"The strike has started," said Audun Ingvartsen, chairman of the Lederne union, on Monday evening.
Oil and gas production will be cut by 89,000 barrels of oil equivalent per day (boepd) as a result of Tuesday's work stoppage, of which gas production will account for 27,500 boepd, Norwegian energy group Equinor said.
For the EU countries, the work stoppage comes at an inopportune time, as they are dependent on more gas from Norway due to a lack of Russian supplies.
Most recently, the trading gas price had risen sharply and doubled within a month to more than 160 euros per megawatt hour (TTF).
According to a calculation by the Reuters news agency, a planned gradual reduction in production by Saturday could result in almost a quarter of Norwegian gas production and around 15 percent of oil production being shut down.
The decision to cut production ultimately rests with the operator Equinor.
The group could not initially be reached for comment.
The Norwegian government said it was following the conflict "closely" and could end the strike in "extraordinary circumstances".
Members of the Lederne union, which represents around 15 percent of offshore workers, had rejected a collective bargaining agreement negotiated by companies and union leaders.
The other Norwegian unions, on the other hand, have accepted him and do not want to go on strike.
The industrial action began at midnight on three fields - Gudrun, Oseberg South and Oseberg East.
From Wednesday it is to be extended to three more fields - Kristin, Heidrun and Aasta Hansteen.
A seventh field, Tyrihans, will also have to close on Wednesday as its production will be processed by Kristin.
Both sides want to intensify cooperation in order to ensure additional gas supplies from Norway in the short and long term, the EU and Western Europe's largest gas producer announced at the end of June.
For example, Russia has stopped deliveries to Poland and the Netherlands, among others, because these countries have rejected the new payment methods in rubles introduced by the government in Moscow.
Due to the supply cuts, Norway has already ramped up its gas production and said it will increase its sales by eight percent this year.
The EU has so far imported around 20 percent of its gas from Norway.
Around 40 percent came from Russia before the Russian invasion of Ukraine on February 24.Keywords: