As Finnish voters head to their polling stations, a close race is expected for three major parties, including the Social Democrats led by Prime Minister Sanna Marin.

Sunday's parliamentary election takes place as high inflation, partly due to the Russian invasion of Ukraine, is increasing strains on the country's economy and fiscal health.

The latest poll published on Thursday by public broadcaster Yle suggests that Marin's Social Democrats, the SDP, is trailing two major rivals with just 18.7 percent support.

Center-right National Coalition, the NCP, garnered 19.8 percent support, while the nationalist Finns Party had 19.5 percent.

The country's ascension to NATO in the coming weeks, has given a boost to the NCP, which has long advocated joining the military alliance.

The Finns party has maintained its support base with its Euro-sceptic policy, and calls for tight immigration controls.

Finland, which shares a border with Russia, had maintained military neutrality for decades, but sought to join the alliance in the aftermath of Russia's invasion of Ukraine.