Norway's top court has ruled that two wind farms in the country's west have violated the rights of Sámi reindeer herders.
Wind turbines on Norway's Fosen peninsula have illegally encroached on the herders grazing land, the court ruled.
Judges at the Norwegian Supreme Court declared that the license for wind power development at Fosen was, therefore "invalid".
However, the practical consequences of the ruling were not immediately clear.
The Roan and Storheia wind farms in western Norway are part of Europe's largest onshore wind energy project and were first unveiled in 2010.
Construction at the two sites by the Norwegian Water Resources and Energy Directorate (NVE) was completed in 2020.
But the project received backlash as the wind turbines were located within the Fosen reindeer grazing district.
Reindeer owners claimed that the development violated their rights to cultural practice, but initially had their appeal against construction rejected in 2013.
However, Norway's Supreme Court ruled on Monday that the rights of reindeer herders had been violated.
Judges said that under United Nations law, ethnic minorities should not be denied the right to "cultivate their culture," such as reindeer herding traditionally practised by the Sámi.
An estimated 80,000 to 100,000 Sámi people live in the Arctic regions of Sweden, Finland, Norway, and Russia.
The construction of the wind turbines in Fosen had "significant negative consequences" on the reindeer's ability to graze, the court said.
Although judges acknowledged that increased renewable energy production is "important," they said that there were less intrusive construction sites for wind farms.
"In this case, there was no question of a collision between environmental considerations and the reindeer owners' right to cultural practice," judges said.
The Norwegian Ministry of Oil and Energy, which had issued the construction permits, said they would study the court's decision before deciding on the matter further.
"This obviously comes as a surprise to us," said Tom Kristian Larsen, managing director of Fosen Vind, one of the operators of the wind farms.
"We have been relying on final concessions given to us by the authorities after a long and thorough process where all parties involved have been heard, and where special emphasis has been placed on reindeer husbandry," he added.
But according to lawyers for the Sámi herders, the court decision should lead to the dismantling of the 151 wind turbines.
"Their construction has been declared illegal and it would be illegal to continue to operate them," Andreas Brønner told AFP.