National is holding out on supporting a bill to ban conversion therapy, calling for amendments to rule out prosecutions for parents.
Meanwhile the Act Party says it will support the bill at its first reading, while also stating "serious concerns" about its potential to criminalise parents, particularly around stopping their own child taking puberty-blockers.
Justice Minister Kris Faafoi announced the Conversion Practices Prohibition Legislation Bill on Friday, to follow through with Labour's election manifesto promise to ban so-called gay conversion therapy.
National's justice spokesman Simon Bridges said the party supported the "intent" of the bill, but would need to see an amendment to rule out prosecutions for parents in order to support it.
Faafoi has said the point of the bill was "not to criminalise people", but he has not ruled it out in interviews. The bill itself indicates parents could be criminalised, and Ministry of Justice officials said in their advice to the Government around a proposed ban interactions within a family would also be captured if they met the proposed definition of conversion practices.
"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.
"This would align with other existing regulatory controls on parental behaviour that could harm children."
Bridges said Faafoi's uncertainty had "caused alarm bells to ring for many New Zealanders".
"Parents are not seeking to harm their children, but decisions around medical transition are very serious and this law would cause unreasonable levels of fear in parents trying to navigate the best outcomes for their child.
"If Minister Faafoi is willing to tighten up some of the loose definitions and add in a parental exemption clause that would protect parents from being prosecuted, National will be able to give the Bill our support."
Act Party justice spokeswoman Nicole Mckee said any treatment to try to change someone's sexuality was "wrong and should be outlawed".
But the law should stick to addressing that issue, she said.
"Instead, this bill overreaches. In its current state it says parents are unable to have a say in whether their pre-pubescent children take hormone blockers if they want to change their gender.
"[Faafoi] has been unable to say whether parents will be criminalised if they stop their own child from taking medication that would take a huge toll on their bodies.
"Parents should be able to parent their children without the threat of being criminalised."
According to the Ministry of Health, puberty blockers, also known as hormone blockers, are medication that halt unwanted physical changes that don't match someone's gender identity.
They are a "safe and fully reversible medicine that may be used from early puberty through to later adolescence to help ease distress and allow time to fully explore gender health options".
On Friday Faafoi said the bill wasn't about criminalising people.
"It is about making sure we prevent harm that is happening as a result of these conversion practices."
Asked whether parents could be jailed if they stopped their child from taking hormone-blockers, Faafoi said anyone intentionally changing or suppressing someone's gender identity or sexual orientation could be breaking the law.
But he told Newstalk ZB there was a "long line" to walk before reaching a criminal offence.
A conversion practice had to be directed towards someone because of their sexual orientation, gender identity or gender expression, and performed with the intention of changing or suppressing their sexual orientation, gender identity or gender expression.
Then harm had to be shown for a child, or serious harm for an adult.
If police decided there was a case, the Attorney-General would then need to sign it off before charges could be laid.
Faafoi was asked again on Monday to clarify the exact details around puberty blockers and if parents would be criminalised for stopping their children taking them, but was unable to give a clear answer.
Instead he reiterated that the purpose of the bill was to stop harm being done to young and vulnerable people, "not to criminalise people".
"It is a very long process before anyone would see the inside of a courtroom."
Labour, the Green Party and Te Pāti Māori have all stated their support of the bill.
The bill will have its first reading in Parliament on Thursday.