National's Chris Bishop urges Jacinda Ardern to 'ask herself an honest question' about Trevor Mallard's behaviour

National MP Chris Bishop is urging Prime Minister Jacinda Ardern to act after House Speaker Trevor Mallard repeated sexual assault allegations under parliamentary privilege.

The Opposition is calling out Mallard for his behaviour in the House after he levelled new claims of sexual assault at a former parliamentary staffer - the same staffer he's previously falsely accused of rape.

"That man's life was destroyed when he sexually assaulted a woman," Mallard told MPs on Tuesday. "That's what did it... I will support the woman and what she said, I will support the investigation that found that he seriously assaulted her... and I will support the police and their investigation and the results of that."

Mallard has been under fire from National since December when it was revealed more than $300,000 in taxpayer money was spent to settle a defamation legal battle with the former staffer.

Bishop, the Shadow Leader of the House, told The AM Show on Wednesday the behaviour was "threatening and bullying".

"Jacinda Ardern needs to really, genuinely ask herself an honest question which is whether she's prepared to tolerate this sort of behaviour from the Speaker.

"To have a Speaker turn up, having settled with someone who he falsely accused of rape - and then continue this attack has just really brought his position into disrepute."

Bishop called on Ardern to act on Mallard's behaviour.

"Jacinda Ardern does honestly need to ask herself if she's prepared to tolerate this sort of behaviour," he said. "If the shoe was on the other foot, if this was a National Party Speaker, what would she be doing? She'd be calling for his resignation.

Trevor Mallard, left, and Chris Bishop.
Trevor Mallard, left, and Chris Bishop. Photo credit: Parliament TV

"We have a justice system in this country. Trevor Mallard's not the judge and the jury of what happens in criminal law.

"What he's done, twice now - is set himself up as the judge and the jury… it's just unacceptable and I say to Jacinda Ardern; the behaviour you walk past is the behaviour you accept."

National leader Judith Collins earlier told The AM Show Mallard's latest outburst makes his position as Speaker untenable.

"It was absolutely the worst, the most disgraceful display from Trevor Mallard that I have ever seen in Parliament in my almost 20 years."

She also called for Mallard to be replaced.

"It's really up to Jacinda Ardern," Collins said. "She's told people that it's really up to Parliament, well it's not."

Ardern's office has been contacted for comment.