Prime Minister Jacinda Ardern says she "totally disagrees" with Israel Folau and how he's using social media.

Asked if his comments should be regarded as hate speech, Ardern told reporters that even if they didn't fit a legal definition they nonetheless could be very damaging.

The Wallabies star faces possible sanction from Rugby Australia after he took to Twitter to tell people to "turn away" from their evil ways after Tasmania became the first Australian jurisdiction to make gender an option on birth certificates.

"The devil has blinded so many people in this world, REPENT and turn away from your evil ways. Turn to Jesus Christ who will set you free," Folau posted.

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The Waratahs Super Rugby star then went on Instagram and warned sinners would be going to hell unless they repented.

Asked about Folau's comments today, Ardern said:

"Obviously at a personal level I clearly don't agree with what he said and very mindful of the fact he is for many a role model, he's a person in a position of influence and with that comes responsibility.

"I'm particularly mindful that young people are members of our rainbow community [and] there's a lot of vulnerability there," Ardern told reporters.

"I totally disagree agree with what he says and how he's using his platform," she said.

Sydney Morning Herald columnist Peter FitzSimons wrote that Folau's latest post should see Rugby Australia cut their ties with the 73-test Wallaby.

"Israel Folau has to go, and will go," the former Australian test player wrote.

"Quick. Clean. Gone. At least until such times as he repents."

"Rugby Australia simply has no choice. They cannot go through one more time the agony of last year when Folau's social media comments trumpeting that gays would go to hell, saw rugby lose sponsors, fans and support," FitzSimons said in the Sydney Morning Herald.

According to rugby.com.au, there was a reported clause in Folau's contract negotiations last year that was specific to his use of social media.

The former league and AFL player, now a rugby union star, created tension on social media last year for his stance on homosexuality.

Six months after tweeting his opposition to same-sex marriage, the Wallabies fullback posted on Instagram last April that gays would go to hell.