That's the $64,000 Question!
In the 2015 election the party got 17.7% of the votes [...] In 2015 they joined the government coalition formed by Prime Minister Sipilä. Following a 2017 split, over half of the party's MPs left the parliamentary group and were subsequently expelled from their party membership.
-Wikipedia
So, to answer your question: Sounds like they do not represent very much of the electorate and are not likely to succeed in getting Finnland out of the E.U.
Regards,
Their party got 9% of the vote, down from 15.5%. But they will gain more votes this year, especially with their anti-EU and anti-refugee platform. Moreover, the percentages matter less in parliamentary systems. We Americans think in terms of our own political system. It is much different from parliamentary, where coalitions are formed and thereby even a minority has much more clout than their percentage. Look at the UK and German governments, where this is very much the game.