Judith Collins has rejected reports the National Party caucus overruled her and deputy leader Shane Reti on who should control fluoridation.
Collins and Reti have previously expressed concern over the Government's moves to centralise decision-making with the Director-General of Health, rather than leave it up to local councils to decide whether to fluoridate their water supply.
"At first blush it looks like an overreach by Government with quite a dramatic change," Dr Reti told Stuff two weeks ago.
While he said he believes in the science - which shows people living in fluoridated areas have better dental health - he doesn't think "the needs, wants and aspirations of local people are trumped by the science of fluoridation".
Newshub political editor Tova O'Brien on Monday reported Collins and Reti tried to make it National Party policy to leave the decision to local councils, but were overruled by the party caucus. MPs from the party told O'Brien it was rare to even have a vote like this, let alone have the party's leader on the losing side, suggesting her days as leader were numbered.
Collins attacked O'Brien on social media, telling her she was "simply wrong" and "entirely wrong", and the story "factually incorrect" in a series of tweets. O'Brien hit back, saying it was based on "multiple sources".
Appearing on The AM Show on Wednesday, Collins said she's "always been pro-fluoridation".
"I've publicly gone out and I've criticised Hamilton City Council back in 2013 for not getting on with the fluoridation... I'm absolutely pro."
In 2013, Collins described Hamilton's move to stop adding fluoride to the water as "bollocks". Less than a year later it resumed fluoridation, after the public overwhelmingly voted for it in a local referendum.
"Simply, the caucus decision was to support the Ministry of Health having control of the fluoridation, but with a proviso that the ministry at least consults with the local district health boards, which I think is perfectly fine. So I just don't know where this story comes from, and I have to say it's highly wrong."
During last year's election debates, Collins said Labour would have her party's backing to wrest control from councils, when Prime Minister Ardern implied then-coalition partner New Zealand First had blocked such a move. Reports at the time suggested Labour did try and get National on board, but caucus chair Gerry Brownlee refused to commit.
Collins told The AM Show the vote in caucus was "unanimous".
"I just don't know why this story's so factually wrong."
Leaks from disgruntled MPs to the media are common when a party is struggling or they're unhappy with the leadership.
O'Brien said in an email she stood by the story, which had "multiple sources".