A new poll for Yle suggests that if a parliamentary election were held now, 26.1 percent of respondents would vote for the National Coalition Party (NCP).
The party, which has advocated for a Nato membership application for more than a decade, has seen its support jump 3.5 percent since the previous poll in March.
The uncertain security situation in Europe brought about by Russia's attack on Ukraine might be one possible explanation.
"When you look at the results week-by-week, then the NCP's support moved to a higher level the week after Russia's invasion and stayed around 26 percent after that," said Tuomo Turja from Taloustutkimus, which carried out the poll for Yle.
"Finns' sense of security has been shaken, and support for joining Nato has increased. The NCP, as the most pro-Nato party, has capitalised on this."
The rise in support comes almost entirely from male voters. Turja interprets that as a signal that security policy is indeed the deciding factor in the rise.
Support for Nato membership is stronger among men than among women.
The biggest drop in support was for the opposition Finns Party, which saw its numbers dip two percentage points compared to last month.
That's as low as the party has recorded since February 2019.
The Social Democrats were the only government party to increase their support, which now stands at 19 percent.
In fourth spot is the Centre Party on 12.3 percent, down 1.1 percentage points since the previous poll. In fifth spot are the Greens on 8.9 percent, down 0.4 of a percentage point.
The Left Alliance is on 8.4 percent, down 0.7 percent, while the Swedish People's Party saw their number dip by 0.6 of a percentage point to 4.2 percent.
The Christian Democrats and Movement Now, both in opposition, saw their numbers decline slightly.