Finland's centre-right National Coalition Party (NCP) and its Swedish counterpart, the Moderate Party, have formed a special Nato working group.
The parties want Finland and Sweden to submit joint applications to the military alliance by the end of June, when Nato hosts a top summit in Madrid, Spain.
The cross-border working group is set to meet for the first time this coming Wednesday in Stockholm.
NCP leader Petteri Orpo said in a statement on Sunday that he has recently been in close contact with Moderate Party leader Ulf Kristersson.
Prime Minister Sanna Marin (SDP) on Saturday said any potential Finnish bid to join Nato would have to be made before summer.