Labour Party members have reportedly voiced their concerns about the handling of allegations of bullying, sexual harassment and sexual assault by a staff member.

The party has held an inquiry into the allegations but it was taken no further.

Newstalk ZB political reporter Barry Soper told Mike Hosking the allegations involved not only sexual assault but rape, offers to pay for sex and that there were 12 alleged complainants.

"What they're saying is, the party is telling them not to comment. They say people incredibly high up are on the side of the accused in the Beehive."

Soper said those allegedly affected were "frightened" of talking to the media as they claimed they would have their support withdrawn if they spoke out.

"They talked about not just sexual assault but rape, they said that this person worked in the Beehive for two years, he was offering promotions for sex. They said there was a huge power imbalance, they said the person was well known to Jacinda Ardern and Grant Robertson.

"They said one victim was hospitalised, two were still working at Parliament, six others were junior party members and there were 12 victims in all."

Soper said the complainants just want the party to be held to account.

He had tried to get comment from Labour Party president Nigel Haworth.

"He said a firm no comment and that was the end of the matter."

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However, Soper said he'd discovered the man at the centre of the allegations had hired a lawyer who told him "that he is innocent, there was an inquiry, he has nothing to answer for and they warned us to leave this issue alone otherwise they will be suing".

Soper said the alleged offender worked for the Labour Party as opposed to Parliamentary Services.

He was unsure when the offending started but there had been mention of a Christmas Party "where bad behaviour occurred".