Documents from a Radio NZ investigation show Philip Morris provided NZ First with a draft piece of regulation which the deputy prime minister at the time, Winston Peters, supported.
They show NZ First assured Philip Morris they would "put that draft into the policy mix".
Mr Peters said the documents referenced were more than six years old, and the attempt to attack NZ First was "old, stale, repetitive, and utterly baseless".
The allegation comes after NZ First list MP and Associate Health Minister Casey Costello led the repeal of the Smokefree Environments and Regulated Products (Smoked Tobacco) Amendment Act 2022.
It effectively scrapped laws aimed at slashing tobacco retailers, removing 95% of the nicotine from cigarettes, and creating a smokefree generation by banning sales to those born after 2009.
University of Otago Aspire Aotearoa Research Centre co-director and public health researcher Prof Janet Hoek said the fact the documents were six years old was "neither here nor there", because NZ First had repeatedly denied having any connections with the tobacco industry.
The revelation raised questions about how easily companies were able to access politicians, and the kind of lobbying that went on behind closed doors.
"The challenge that he [Mr Peters] has to address is that there have been allegations that he’s been dealing with tobacco companies and using their documents to inform policy.
"None of his statements, none of his rebuttals, address that concern.
"What we need is some transparency — some actual evidence showing that these allegations that have been put forth in the documents don’t stand, and that’s not what he’s been able to provide.
"I think he really needs to be held to account here."
She said Mr Peters’ instinctive response was "attack is the best defence".
"I think there’s actually a real question about integrity of the political process here, and what people want to feel is that politicians are acting in the best interest of the country, not the best interest of the tobacco company."
Prof Hoek said the "discrepancy" was further decreasing trust in the government, and called on Prime Minister Christopher Luxon to assert some leadership and removed the tobacco and vaping portfolio from NZ First, and entrust it to a politician without alleged links to tobacco giants.
"We know that tobacco companies operate in the shadows by lobbying politicians.
"What these documents reveal are claims that tobacco companies are not just lobbying, they are writing policy.
"The New Zealand public will be disgusted to learn that is how the party that should be promoting public health is allegedly behaving."
Fellow Aspire co-director Prof Richard Edwards said the repeal of New Zealand’s world-leading smokefree legislation prompted a huge outcry from communities affected by smoking, health organisations, health professionals and public health experts.
"The repeal raised questions about influence of the tobacco industry.
"Subsequent industry-friendly policies like tax cuts for heated tobacco products only increased those concerns, and the recent revelations of close links between NZ First and Philip Morris suggest these concerns were well-founded."
He called for the urgent reintroduction of the repealed measures, which were very likely to rapidly reduce the enormous harm from smoking, and protect future generations from smoking.
Asked to respond to the accusations, a spokesman for Mr Peters pointed to a social media post online.
In it, Mr Peters said the documents referenced were more than six years old, and the "attempt to attack NZ First is old, stale, repetitive, and utterly baseless".
He said multiple government departments had themselves proactively reached out to "big tobacco" for direct feedback and advice on tobacco legislation.
He accused Radio NZ of being "clearly lefty biased", and their "bottom-of-the-barrel attack reporting" had caused New Zealanders to lose trust in them and switch to other stations.
"The smokefree legislation that we implemented is working," he said.
"New Zealand First is proud of the smokefree legislation, which is backed by Action for Smokefree 2025 (ASH), that we have implemented and that we are still implementing."
