Prime Minister Sanna Marin's Social Democratic Party has formally backed Finland's Nato membership.
The largest parliamentary group's party council met for several hours on Saturday afternoon in Helsinki. The 60-member council gave the green light to a Nato bid by a vote of 53–5 with two abstentions.
The vote was expected after a unanimous 'yes' vote by the party board and Marin's own support for a Nato application.
"As a result of the significant change in the security environment in Finland and Europe, the SDP supports Finland's membership in the Nato," the party council said in a statement in the late afternoon.
Following the decision of the SDP party council, President Sauli Niinistö and the government's Committee on Foreign and Security Policy are to discuss Finland's application for Nato membership on Sunday. Parliament will convene to consider the Nato application on Monday.
Marin: Finland, Sweden to apply together next week
In her address to the party council on Saturday, Marin said that "Finland and Sweden have been Nato's closest partners for years. We are technically very compatible and train regularly with Nato countries. However, we are not covered by Nato security guarantees."
"Here is the essence of our decision: would Nato membership increase Finland's security in the changed situation? Would Finland's membership in Nato strengthen European security? The answer is that it would," Marin said.
"I believe that Nato membership is the best solution for maintaining Finland's security and the stability of our neighbouring areas in the changed security policy situation. That is why we should apply for Nato membership without delay."
In an interview with the daily Helsingin Sanomat published on Saturday, Marin said she expects Finland and Sweden to apply for Nato membership together next week.
Swedish Prime Minister Magdalena Andersson's Social Democratic Party is likewise expected to approve that country's Nato application on Sunday.
Marin said that she has personally backed membership since 2020, although she only formally announced her stance in a joint statement with President Sauli Niinistö on Thursday.
Nearly all SDP MPs to vote yes
Antti Lindtman, chair of the SDP parliamentary group, said that MPs will be given a free hand to vote their conscience on the issue.
Yle has learned that nearly all of the SDP's parliamentary group intends to vote in favour of the Nato application. Only two of the SDP's 40 MPs are expected to vote against it.
Government partners the Left Alliance are the only other party that has not yet announced its Nato stance. They may end up being the only major party to oppose membership, but do not intend to quit the government over the issue.