National leader Judith Collins has declared the Government "anti-parents" over a law that will ban controversial conversion practices.
Under the law, performing conversion therapy intended to change or suppress someone's sexual orientation, gender identity, or gender expression could result in a prison sentence of up to five years.
National stood alone last week as the only party not to support the legislation, over concerns parents could face charges for preventing their children from taking hormone blockers - medication to delay unwanted physical changes that don't match gender identity.
"Under this law, if a mum tells her 12-year-old son or daughter, 'before you go on puberty blockers or other hormone treatment, wait till you're 18', that mum will be breaking the law," National MP Simon Bridges said in Parliament.
It came after Justice Minister Kris Faafoi was repeatedly unable to confirm if the conversion therapy ban applied to parents telling their kids not to take hormone blockers.
There are signs not all in National's caucus agreed with voting against the legislation, after what appears to be a private Twitter message National MP Chris Bishop had with an unknown person, was leaked.
"Hated your vote on conversion therapy," the person says to Bishop, to which he responds, "Yeah. Me too."
Collins told Magic Talk Bishop was expressing the frustration shared by the entire caucus - that they wanted to vote in favour of banning conversion therapy, but not if parents could be prosecuted.
"Chris had some text or some sort of message discussion with someone who he considered a close friend and that friend was obviously some sort of far-left activist by the look of it. I apologise if I'm wrong on that one, but I can't imagine anyone not being like that doing that," she said.
"He's saying exactly what a lot of us have said in the caucus. Earlier in the year, we said we would support a ban on gay conversion because we believe it is a pseudoscience. The whole caucus was very happy to sign up to that.
"But the Bill that the Government put forward actually enabled parents to be criminalised and it was very important for us that, when you're looking at the first reading of the Bill, that's all about intent."
The Greens, ACT and the Māori Party all supported the legislation through its first reading, to then hash out any concerns during the select committee process. But National voted against it, to highlight its concerns for parents.
"Look, every other party in Parliament signed up to vote for it in the first reading,” Collins said, "but I'm buggered if I'm going to vote for anything that criminalises parents trying to give advice to their kids."
ACT MP Nicole McKee raised similar concerns about the potential for parents to be charged under the law.
She pointed to the impact statement, which reads: "It would be a criminal offence for parents or other members of a family to attempt to change or suppress the sexual orientation, gender identity or expression of children within the family."
But ACT voted in favour, McKee said, because "on the face of it, and with what we believe to be an understanding of the intent of the Bill, we want to support this".
Collins said National took a different approach to make its position known.
"It's already going to select committee. We've only got 33 votes and there's an overwhelming majority to get it there. But we want to make it really clear to the Government and their anti-parenting type behaviour, and anti-parents frankly, that we will not stand by and allow this to happen without making such a song and dance about it that the whole of the public knows.
"No one would be talking about it now if we hadn't stood up for parents."
Justice Minister Kris Faafoi said the Government was willing to listen to concerns.
"We will take the select committee very seriously. We will watch those submissions, we will watch the submissions and the tone of the submissions that are made by other political parties, and we will make this Bill better if we think we can."