The allegations, published in a column online in the NZ Herald this afternoon by Hamilton West MP Dr Gaurav Sharma, have been described as "extraordinary" and "brave" by Opposition MPs.
Senior Labour ministers have also said they had not seen any bullying between MPs in the party.
In the column, Sharma took aim at Parliamentary Service, the party whips' offices and leaders, saying bullying was "rampant."
Parliamentary Service Chief Executive Rafael Gonzalez-Montero revealed they had been working through "employment matters" involving Sharma.
"The Parliamentary Service works alongside whips from all parties," he said.
"This has included working closely with the Labour Whip's office over the past year to address employment matters with Dr Sharma.
"We do what we can to support all our MPs, and we acknowledge the triangular employment relationship at Parliament is complex.
"It is also important to make it clear that the Service cannot direct MPs what to do and how to act.
"MPs are elected representatives of New Zealand's citizens as that would impinge on New Zealand's democracy, and the free right of MPs as elected representatives of New Zealand's citizens."
Labour Whip Duncan Webb also said they'd been working with Parliamentary Services to address employment matters in Sharma's office.
"We had been working to provide support for Gaurav and find a solution. We're committed to reaching an outcome everyone is happy with."
Speaker Trevor Mallard said he would not discuss individual MPs or staff relationships.
"A practice was developed during the last Parliament and has continued into this Parliament where MPs who have ongoing staff relationship issues have been delayed in their appointment of new staff until the whips and Parliamentary Service are convinced they have sufficient skills to properly supervise them," he said.
Since writing the column Sharma has refused to comment further except only to mention: "I am not the bully."
When asked who the bully or bullies were, Sharma said: "We'll find out."
Asked about cases where an MP was allegedly bullied by another MP, Mallard said he expected to soon announce a new Commissioner of Parliamentary Standards, who would investigate allegations.
He said MPs and staff could go to the Commissioner if they were unsatisfied with the way a complaint had been handled.
National MPs meanwhile were quick to leap onto discontent on the Labour backbench, taking attention away from the misdeeds of their own MP Sam Uffindell, which has dominated headlines this week.
National MP Chris Bishop described Sharma's allegations as "extraordinary".
"Dr Sharma is a very brave man to take a swing at both the Prime Minister and the Deputy Prime Minister, they're extraordinary allegations for the Labour Party to answer," Bishop said.
"He talks specifically about the Prime Minister's office and the whip's office of the Labour Party in his article. He's clearly had a very tough time here and it's very brave of him to speak out," he said.
National Party whip Chris Penk did not respond to broader criticism of party whips and only said "Labour's leadership will need to respond to these allegations about a lack of kindness".
National MP Matt Doocey said: "I'm not sure why he's throwing his own whip's office under the bus."
Labour MPs so far have not supported the claims by Sharma, a first-term MP.
Senior Labour ministers Chris Hipkins and Willie Jackson both said they had not seen any bullying between MPs in the party.
"Never seen it in my life - we're a great whānau," Jackson said.
Fellow first-term Labour MP for Illam Sarah Pallett said she did not share the experience of Sharma.
"I've had a lot of support and that's all I have to say."
Pallett, who sits next to Sharma in the House, said he had "always been a friend of mine" but had not confided any of the details outlined today with her.
MP Dr Emily Henderson said she hadn't read Sharma's piece but hadn't experienced bullying within Parliament.
"What I've experienced is a bunch of people who have taken great heed of the Francis report and working very hard," the MP for Whangārei said.
The Francis Review into the Parliamentary workplace was done by Debbie Francis in 2019 and found bullying and harassment was systemic and there was low accountability for bad behaviour - especially for MPs.
Changes since then include a code of conduct and attempts to address MPs who have repeated issues with staff.
Sharma, who worked as a general practitioner, has been in Parliament since winning the Hamilton West seat from National's Tim Macindoe in 2020.
He said despite an extensive review into bullying at Parliament and steps to handle complaints better, there was still no adequate process to deal with MPs bullying other MPs.
He took aim in his column at Parliamentary Service, claiming it worked "behind the scenes" with the party whips, party leader's offices and even the Prime Minister's office.
"Where concerns have been raised with Parliamentary Service about staff or MP colleagues showing unacceptable behaviours in some cases there does not appear to have ever been any investigation or an intent to investigate," he wrote.
"If anything, in my experience, when an MP raises serious concerns the Parliamentary Service steps back, stonewalls the conversation, ghosts the MP and throws them to the Whip's Office to be gaslighted and victimised further so that the party can use the information to threaten you about your long-term career prospects."
Among Sharma's accusations were that "you can go weeks and months before getting a reply to urgent issues".
"When they do have an answer it is seldom in writing and often from behind the desk of the party whips who - in my opinion, and based on what I have seen in my time in Parliament - use the Parliamentary Service to bully and harass their MPs 'to keep them in line.'"
He said "parliamentary staffers are leaving in droves" as a result.
