Helsinki (AFP) - Finland's parliament is on Friday expected to vote for a second time on same-sex marriage, just two weeks before a 2014 law enshrining it was due to take effect.

The re-vote is a last-minute attempt by opponents to prevent legalisation of same-sex marriages in Finland, but is seen as having little chance of succeeding.

Finland's previous parliament passed a law on "gender-neutral marriage" in late 2014, and it was due to take effect in early March this year.

But conservative opponents -- who have called for a "Genuine Marriage" law recognising marriage as solely being between a man and a woman -- resorted to a citizen's initiative, gathering more than the 50,000 signatures required for parliament to debate an issue.

Parliament's legal affairs committee rejected the counter-motion on Tuesday, but conservative members from the Christian Democrats and the populist Finns Party, one of the three members of the government coalition, insisted on having the plenary vote on it.

"It would indeed require a small miracle for the Genuine Marriage to win," Antero Laukkanen, one of the initiative's supporters and a lawmaker from the Christian Democrats, told Finnish news agency STT.

Others have accused the initiative's proponents of grandstanding for voters ahead of municipal elections in April and of wasting parliament's time on a futile vote.

"I personally apologise to rainbow families who will have to listen to the matter being debated once more," Centre Party MP Mikko Karna wrote in a statement.

Finland has recognised same-sex partnerships since 2002, but has until now remained the only Nordic country where gay marriage is not legal.

The Finnish legislature approved the law in 2014, after a second vote, by 101 votes to 90.