Timo Soini (left) debated with Centre Party leader and prime minister Mari Kiviniemi this week Finns have gone to the polls to elect a new parliament in a vote that may affect future EU bail-outs if a rising nationalist party does well.
Opinion polls suggest the True Finns have nearly quadrupled in popularity since the last election though they are unlikely to enter government.
Analysts see mainstream parties taking a harder line on the EU as a result.
Unlike other eurozone states, Finland can put requests for bail-out funds to a majority vote in parliament.
Since any bail-out must be approved unanimously by all 17 eurozone members, a hostile Finnish government could theoretically veto it.
The outcome of Sunday’s election may affect EU plans to shore up Portugal as well as impacting on stability in debt markets.
Polling stations in the Scandinavian nation of 5.3 million people opened at 0900 (0600 GMT) and are to close at 2000, with first results expected to be announced around the same time.
Finland is currently governed by an EU-friendly four-party coalition led by Prime Minister Mari Kiviniemi’s Centre Party and the conservative National Coalition Party (NCP).
Opinion polls suggest the NCP will have a narrow lead, just ahead of the Centre Party and the opposition Social Democrats, making a new coalition the most likely outcome.
“The bigger parties have no reason to invite the True Finns into any coalition if they can make up the numbers without them,” Olavi Borg, professor emeritus in political sciences, told the Associated Press news agency.
Polling organisations have given the True Finns more than 15%, a leap from the 4% they actually won in 2007.
With its charismatic leader Timo Soini, the party rejects rescue funds for EU “squanderers”, as well as opposing immigration.
Analysts say many Finns have become disenchanted with the big three mainstream parties who have run the country for decades.
“Whether the True Finns will really [emerge] as champions of the elections is still uncertain but I think we will clearly get a more nationalistic, more conservative, less European-oriented government in Finland,” ING senior economist Carsten Brzeski told Reuters news agency.
This article is from the BBC News website. © British Broadcasting Corporation, The BBC is not responsible for the content of external internet sites.