Russian energy supplier RAO Nordic says it will suspend deliveries of electricity to Finland from Saturday, citing problems with payments.
The company said it had not been paid for previous deliveries.
The Finnish grid operator said Russia provided only a small percentage of the country’s electricity and that it could be replaced from alternative sources.
On Thursday, Russia threatened to take “retaliatory steps” after Finland said it planned to join Nato.
Finland shares a 1,300-km (810-mile) border with Russia, and has previously stayed out of Nato to avoid antagonising its eastern neighbour. However, since Russia’s invasion of Ukraine there has been a surge in public support for Nato membership.
On Sunday Finland is expected to formally announce its plan to join.