Parliamentary workers who complained about inappropriate behaviour in the Labour Party are fearful, intimidated, and feel they have not been taken seriously, says National Party deputy leader Paula Bennett.

Bennett said she had been contacted by one of the women who made a formal complaint with the Labour Party, one of several who alleged bullying and sexual harassment about a Labour staffer working in the parliamentary complex.

"She had made formal complaints, as had a number of other people over many months, has not been taken seriously, has not had due process," Bennett told reporters this afternoon.

"They've have been told to keep quiet about what's going on, that it should be kept as an internal process, advised not to go to the police. They feel they are losing all options and actually losing hope."

Bennett said she was told the complainants, some of whom worked in the Beehive and in the Prime Minister's office, were feeling unsafe.

"They're at the stage now where they're seeing people having panic attacks, crying, really serious anxiety. They've taken the extraordinary step, because they feel they are not being listened to or taken seriously, to actually come to the deputy leader of the Opposition to hope they can be heard."

Prime Minister Jacinda Ardern confirmed on Tuesday that the party conducted an internal investigation into the complaints, but that process was now being reviewed independently following further complaints.

"We need to be open to the fact that we don't always get it right," Ardern said on Tuesday.

She added that anyone with complaints "of that nature" should go to the police.

The Herald understands there are 12 people who alleged improper behaviour, seven of whom laid formal complaints with the Labour Party. Four have since quit the party.

No disciplinary action was taken following the internal investigation, and the complainants had not laid any complaints with the police or with the Speaker, who is responsible for the health and safety of parliamentary workers.

Bennett did not want to comment on the nature of the allegations, but she had raised her concerns with Speaker Trevor Mallard.

"I'm not sure what they talked about would cross a criminal threshold," Bennett said when asked about the possibility of laying a police complaint.

"It would certainly cross a unacceptable behaviour within the workplace threshold ... People have a right to come to work and feel safe."

Bennett said she was told that the complainants now felt they were the subject of a witch-hunt because some of them had contacted the media.

"That is actually causing a lot more anxiety. They talk about intimidating behaviour. They have absolutely no faith in the process that will come from the Prime Minister's office."

Bennett demanded more from Ardern.

"She talks about leadership and actually providing a safe environment, and I believe action needs to be taken immediately.

"I believe these people actually work in her office and work in the Beehive, and as such that is not just a party matter. That is a employment issue that is within her own office."

Bennett said if the alleged victims had been told not to go to certain areas in Parliament to avoid running into the alleged perpetrator, that would be "appalling".

"They are literally fearful and told to avoid the person that's causing that for them."

Bennett did not think the woman was "playing politics" by coming to her, but was simply desperate to be heard.

"I hope by speaking out that it gets a level of seriousness that it deserves."

Labour was rocked last year with allegations of indecent assault at a Young Labour summer camp.

Ardern said the current review was a chance to see what, if anything, the party should be doing differently.