Finland's ruling Social Democratic Party was expected to announce on Saturday their support for joining the NATO defence alliance.
Finland's President Sauli Niinistö and Prime Minister Sanna Marin endorsed joining NATO "without delay" earlier this week, saying it would strengthen the Nordic country's security.
An endorsement by Marin's Social Democrats would mean that a broad majority in the Finnish parliament are in favour of joining, paving the way for a membership application in the coming days.
Finland, which shares a 1,300-kilometre-long border with Russia, has seen public support for membership soar since the Kremlin's war against Ukraine erupted in late February.
Denmark, Norway and Iceland have been members of NATO since its founding in 1949. Sweden, which like Finland is not a member, is also considering applying.