Russia cut off natural gas deliveries to Finland on Saturday morning, following a dispute about rouble payments with Russian state-owned company Gazprom.
Finnish energy provider Gasum had already announced on Friday that gas deliveries were to be suspended.
According to Gazprom, Gasum was not paying in roubles as demanded by Russian President Vladimir Putin.
Gasum confirmed the suspension on Saturday and said customers will receive gas from other sources through the Balticconnector pipeline, a statement said.
The pipeline connects the Estonian and Finnish gas grids.
According to Gazprom, Finland received two thirds of its gas from Russia last year, amounting to a total of 1.49 billion cubic metres of gas.
The Finnish company had previously said that it would not accept Gazprom's demands to settle payments in roubles. The two companies also disagreed on other issues.
Gas makes up only about 5% of Finland's energy mix, according to the Finnish Broadcasting Company. However, almost all of it comes from Russia.
Gasum said it is the only energy company in Finland that buys gas directly from Russia's Gazprom.
Moscow's move marks a rise in tensions with its Nordic neighbour, which this week officially applied for membership in the NATO defence alliance.
Last month, Russia also froze gas supplies to Poland and Bulgaria because they had failed to make payments in roubles in line with Moscow's demand, which is seen as a tactic to boost the value of the local currency amid tough Western sanctions on the economy due to the war in Ukraine.
'No reason to panic'
Minna Ålander, a Finland expert at the German Institute for International & Security Affairs, said this was "no reason to panic" and that the supply cut had been anticipated for weeks.
"That Russia is now stopping energy supplies to Finland is part of their bigger bullying scheme towards EU member states," Ålander wrote on Twitter. "It’s just that the strategy backfires in the Finnish case because Finland doesn’t depend on Russian energy."
Jukka Leskelä, chairperson of the Finnish Energy Industries Association, also doesn't expect supply problems this summer.
"There is still a lot of time before the fall and winter. The situation has changed a lot," Leskelä told the Finnish news agency STT. "Many companies have already taken safety precautions and are looking for alternatives to Russian gas."
On Wednesday, citing Europe's altered security landscape following Russia's invasion of Ukraine, Finland and Sweden submitted applications for NATO membership.
Russia had promised a response, but whether there is a connection with the energy cut-off is unclear.