Paula Bennett claims to have been contacted by a Beehive staffer who alleges to be "one of the victims of a perpetrator", and says their complaints haven't been taken seriously.
Bennett, deputy leader of the National Party, said on Thursday the woman - along with "a number of other people" - has laid complaints over many months.
She said the victim claims to have not been taken seriously by the Prime Minister's Office and has spoken of feeling "extremely unsafe and actually fearful".
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"She expressed to me that they're at the stage now where they're seeing people having panic attacks, crying, and really serious anxiety," Bennett said.
"They've taken the really 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 that they can be heard."
Bennett said complaints were made to both the Prime Minister's Office and the Labour Party, and that the complainants have been told to keep quiet.
"They now feel like there's a witch-hunt on to find people who have spoken to the media and Newshub earlier this week," Bennett said.
Newshub revealed on Monday that Labour has been forced to review an internal investigation into bullying, sexual harassment and sexual assault by a Labour staffer.
The complainants told Newshub the party had done nothing to improve its processes since the sexual harassment allegations at last year's Young Labour summer camp.
It's unclear whether the person who went to Bennett is one of those involved.
When asked what Prime Minister Jacinda Ardern should do about the situation, Bennett said: "Well, she talks about leadership, and actually providing a safe environment, and I believe that action needs to be taken immediately."
Bennett added: "I believe that these people actually work in her office and work in the Beehive and as such that is not just a party matter that is an employment issue that is within her own office."
Ardern said on Tuesday morning that it "hasn't been raised as an employment issue but rather a party one".
In a statement to Newshub, the Prime Minister said she's been advised that none of the people who made a complaint to Labour about a party member currently work in any part of Parliament.
She said if a complaint were made about someone in the workplace, "that would be dealt with immediately as an employment issue".
"While to the best of our knowledge no such complaints have been raised we have sought to proactively offer support to staff."
Ardern added: "We continue to urge anyone with concerns or anyone who might feel unsafe to raise that either with their line manager, parliamentary service or ministerial services.
"To the best of our knowledge, the issues raised by Ms Bennett have not been raised with us, Parliamentary or Ministerial Services."
Bennett said she's not sure what the complainant described "would cross a criminal threshold, but it would certainly cross an unacceptable behaviour in the workplace threshold".
"I've spoken to the Speaker myself and expressed that I believe that he as the head of Parliament, has an obligation to provide a safe work environment," she said.
"If anyone else wants to come and speak to me, I will absolutely keep their confidence."