The Green League held a defiant party council meeting over the weekend with Anni Sinnemäki, party leader and labour minister, departing from her prepared speech by saying that the fight against the True Finns was an important feature of the Greens' general election campaign.
Sinnemäki said voters would choose between an open Finland and a closed Finland.
The True Finns, a party that rides on an immigration-critical platform, has overtaken the Greens to become the country's fourth-largest party in terms of poll ratings.
Sinnemäki accused the True Finns of playing to the public's fears.
Ville Niinistö, the chairman of the Greens' parliamentary group, said some of the True Finns resorted to rhetoric that was exactly the same as that deployed by the Sweden Democrats.
"Many True Finns hanker after a monolithic Finland where everybody must be the same."
Oras Tynkkynen, a Green MP and climate aide at the prime minister's office, spent his entire speech blasting the True Finns, pointing to a contradiction in the party's proposal to cut foreign aid and its goal to reduce immigration.
Among motions approved by the party council was a proposal to lift mandatory Swedish-language tuition in eastern Finland.
In another controversial proposal, the party council proposed doing away with Swedish language exams for civil servants.
Sinnemäki and Tuija Brax, the justice minister, distanced themselves from the two proposals Timo Soini, the True Finns leader, said the "Green elite" was nervous about changes they would likely face at the general election.
"By mounting the attack the Greens are trying to mask their own failure in the nuclear power decision," Soini said in a statement Sunday.
"The Greens have managed to dupe the old parties into backing their cost-raising energy policy."