The Minister for Women is standing by Prime Minister John Key, after he was forced to apologise to an Auckland waitress for pulling on her ponytail.

Rosie cafe worker Amanda Bailey, 26, wrote an anonymous blog on Wednesday, claiming the Prime Minister had pulled on her hair numerous times over many months when he visited with his wife Bronagh.

Key apologised for his actions, saying he initially thought of it as "banter" and "a bit of horseplay". He said he apologised when it became clear Bailey did not appreciate his advances.

Ross Giblin Minister for Women Louise Upston is standing by the Prime Minister, who has apologised for repeatedly pulling a woman's ponytail

Since then, Key has faced international ridicule and a chorus of condemnation from opposition MPs, women's rights groups and lawyers, as well as Human Rights Commissioner Jackie Blue.

But while Women's Minister Louise Upston released a statement repeating Key's apology, she refused to comment on issues of women's rights in the workplace.

"As the Prime Minister has said his actions were intended to be light-hearted. It was never his intention to make her feel uncomfortable," she said.

"He said that in hindsight it wasn't appropriate, and that is why he apologised."

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Key's behaviour has been described by many as "weird", and others as sexist. In her first blog, Bailey said she felt like she was the target of a "schoolyard bully".

Labour leader Andrew Little said the incident did not match the standards expected of a prime minister.

NZ First leader Winston Peters has suggested Key has a hair fetish, while saying he could face criminal charges.

Peters said Key pulling Bailey's hair was "inexplicable".

"It's not conduct becoming of any gentleman."

Asked what he thought of Key's actions, Peters responded: "You know what a trichophiliac is, don't you?"

"A trichophiliac is someone with a hair fetish."

Peters questioned what Key's bodyguards were doing while Key was bothering Bailey.

"When you read what that woman has written, she is entitled to her human rights - but no one is giving them to her, by the looks of it."

The police had been put "in a most invidious position," Peters said.

"In the case of an assault, you don't need a complainant, you just need the evidence."

"And if you look at the elements of an assault, this, on a prime facie case, is there."

A police spokesman said police were not currently investigating the matter.

Peters said Key's apology "doesn't cut it", and it was inappropriate that he had given Bailey two bottles of wine after the incident.

'REDUCE SEXISM'

In an open letter, The National Council of Women said Key had "crossed the line", even if his antics were "well-intentioned".

"Now your eyes have been opened to how easily sexism can occur, we call on you, as Prime Minister, to do more to reduce sexism and its effects in New Zealand," council chief executive Sue McCabe said in an open letter to Key.

She said Key's apology was appreciated but his hair-pulling was a symptom of a wider culture of casual sexism.

"We don't see this as an isolated case and the real story is not about you. Rather, the fact that our Prime Minister has joined the list of people outed for sexism highlights how much sexism is a part of our culture. And it starts at the top," McCabe wrote.

The Human Rights Commission backed the council's letter and Blue - a former National MP - said it was "never OK to touch someone without their permission."

"Talking about what's acceptable and what isn't is a conversation worth having and one every New Zealander needs to be part of."

Women's rights campaigner and former National Party MP Marilyn Waring said on Radio New Zealand Key's conduct amounted to sexual harassment.

But while Upston refused to comment on the issues raised by her party's leader, National MP Judith Collins said Key "overstepped the mark".

Collins told Paul Henry's breakfast show, while she believed Key's apology was genuine, she felt "a lot of sympathy" for Bailey.

In a second blog post on The Daily Blog, Bailey stood by her decision to go public.

"The public had a right to be aware of how poorly their Prime Minister had behaved".

KEY SHOULD BE 'HELD TO A HIGHER STANDARD'

The National Party caucus needs to look closely at the Prime Minister's behaviour when his actions could trigger a Police and Human Rights Commission complaint and an employment dispute, says the Greens.

John Key should be judged by the same high standards that have been the "downfall of MPs and state sector bosses", Green Pary co-leader Metiria Turei said.

"Backbench MP Aaron Gilmore lost his job for abusing a waiter, and Former CERA chief Roger Sutton lost his job for behaving in a way that women in his office found offensive.

"The Prime Minister of New Zealand should be held to a higher standard than either of them, the problem is he's only answerable to himself."

Key was clear that hospitality staff should be treated with respect when he "came down hard" on Gilmore for his inappropriate behaviour towards a waiter, Turei said.

"Arguably, John Key's repeated harassment of the Auckland waitress is even worse than Gilmore's one-off drunken rant."

She said Key needed to lead by example and needed to respect workers and women.

Meanwhile, other senior Ministers also appeared reluctant to comment.

Education Minister Hekia Parata would not be drawn on the incident.

"I don't want to get into commenting on this, there are enough people commenting on it already."

It has since emerged serial litigant Graham McCready has lodged a sexual harassment complaint against the Prime Minister.