With 23.4 percent support, the main opposition National Coalition Party (NCP) was still Finland's most popular last month, according to Yle's monthly survey, published on Thursday.
Tuomo Turja, director of polling firm Taloustutkimus, told Yle that support for the party was still "unusually high" in July, noting that similar numbers last occurred for the NCP in 2011, when the country had four medium-sized parties.
June's survey saw the NCP's support fall slightly, amid allegations that one of its MPs, Wille Rydman, had harassed women.
SDP's support exceeds 20 percent
Prime Minister Sanna Marin's Social Democratic Party came in second place in July, with 20.3 percent support.
The party has not seen a decline in its approval ratings in surveys despite recent troubles with majority state-owned energy company Fortum and its German subsidiary Uniper, which Finland's Minister of Ownership Steering, Tytti Tuppurainen (SPD), had to explain.
Centre Party loses supporters
The latest voter survey saw another dip in support for the Centre Party, which has seen its backing among voters decrease by 2.5 percentage points since April.
Previous Centre supporters appear to be moving into the NCP camp, Turja noted, adding that the survey showed them also drawn to the Finns Party — both of which are in the opposition.
"This may not be due to any clear policy issue," Turja noted.
Support for the Finns Party has been on a slight upward trend over the summer. The third largest party in the country, it saw its support among voters rise by one percentage point in the latest poll.
Taloustutkimus interviewed nearly 3,000 people between July 6 and August 2. Just below 2,000 respondents expressed support for a party. According to the pollster, the margin of error is plus or minus 1.8 percentage points in either direction.