A window at the Finns Party's office in the southwestern city of Turku was smashed on Monday night.
Hannu Maja, chair of the party's Turku branch, told Yle that eight large stones were found on the street in front of the office on Tuesday morning.
In addition to the broken glass, a sticker with the words 'rasistipellet' — roughly translated as 'racist clowns' — was found on the door.
Maja said she has reported the damage to police in the city.
"This is a very serious matter and I condemn it very strongly. People should be able to be involved in politics completely freely, and I hope that all parties will condemn such behaviour in the strongest possible terms. This is not part of politics," Maja said.
She added that the Finns Party's office in Turku is vandalised in some way on a monthly basis.
"Someone or some people go and write 'greetings' on the windows. This is unfortunately common and seems to be becoming more and more common," she said, adding that only the more serious acts are reported to police.
The latest incident was first reported by local newspaper Turun Sanomat.
