New Zealand opposition MP Tim van de Molen has been sacked as National's defence spokesman and will be censured by parliament after threatening a Labour MP.

On Thursday, parliament's privileges committee found Mr van de Molan was aggressive, hostile and unprofessional towards Northcote MP Shannan Halbert during a transport committee hearing in June.

The committee found Mr van de Molan, frustrated at his lack of questions during the hearing, walked over to him, stood over him and told him to "Stand up mate" before blocking the exit.

"It was really intimidating at the time," Mr Halbert said.

Parliamentary staff were so uncomfortable they considered ringing security during the 30-second incident.

Labour referred the behaviour to the privileges committee after Mr van de Molen refused to apologise, both on the day, and in days afterward.

He did so after the report of the committee, which used an independent barrister, was tabled.

"Although I have a different recollection of some aspects of the incident, I completely accept the findings of the committee," he told parliament.

"I apologise to all those who were in the room but specifically to Mr Halbert, who was most impacted by my conduct.

"I am horrified at the thought of my conduct having been perceived as threatening."

Mr van de Molen, a two-term MP, endured personal tragedy in April when his younger sister was killed in a quad bike incident.

He also missed three months of parliament last year after a horrific chainsaw accident when a branch fell on his scaffolding.

"I've had a difficult time losing my sister and breaking my neck, back and arms is difficult for anyone to go through, but there's no excuse and in my mind (those experiences) have not had an impact on this behaviour," he said.

Opposition leader Chris Luxon was notified of the decision on Tuesday and stripped Mr van de Molen of his portfolios after a discussion on Thursday morning.

"We've taken it incredibly seriously," he said.

"Tim could have apologised much sooner and much quicker and that was poor judgement."

Mr Luxon defended not disendorsing Mr van de Molen, saying it was "not a sackable offence" and his sanction was proportionate.

"Everyone makes mistakes and there is a path back for Tim," he said.

Mr van de Molen will be censured by parliament next week.