The leadership of Sweden's ruling Social Democrats will hold an extra meeting on May 15 where they could decide if the party will switch policy and support an application to join NATO, party secretary Tobias Baudin said on Wednesday.
With a majority in parliament backing joining the alliance, the Social Democrats, the biggest party in every election for the past 100 years, are seen as the major obstacle to an application.
"The party leadership could choose to make a decision then," Baudin told news agency TT.
Russia's invasion of Ukraine, which it calls a "special operation", has forced a rethink of the security policy in Sweden and Finland, both of which stayed out of NATO during the Cold War.
Both countries are expected to make a decision about whether to apply to the 30-nation alliance in the coming weeks.
Sweden's parliamentary parties are conducting a joint review of security policy which is expected to report on May 13.
The Social Democrats are conducting a separate policy review.
Previously, the party has said it would announce a decision at the latest by May 24, when the leadership is due to hold a meeting.
However, Sweden is coordinating with Finland - its neighbour and closest defence partner - on the question of NATO membership and Helsinki is seen as moving more quickly than Stockholm.
Swedish Prime Minister Magdalena Andersson has said the two countries will make separate decisions, but that what Finland decides will have a big impact on Sweden.
(Reporting by Simon Johnson and Johan Ahlander; Editing by Sandra Maler)
