Prime Minister John Key has rejected ACT leader Don Brash's suggestion that marijuana should be decriminalised.
Dr Brash said in a weekend speech the drug was relatively harmless and prohibition was ineffective and expensive.
But Mr Key, whose government runs strong anti-drugs policies, said that wasn't what the public wanted.
"Ask parents if they want their children smoking a joint before going to school," he said on TV One.
"There's no place for drugs in our society. We've got to stand up and say we don't want drugs."
ACT has also strongly opposed drugs in the past and Dr Brash's comment surprised other parties.
He said he was expressing a personal opinion, but it has been taken as an indication ACT could change its policy after the election.
Some have accused ACT of pushing the self-destruct button with the call, however. In addition to Dr Brash's new views, second-in-command John Boscawen is quitting politics.
The Green Party says Dr Brash is making a brave move by supporting the decriminalisation of cannabis.
Greens co-leader Metiria Turei says it shouldn't come as a shock.
"I think people are surprised they're turning it into their dominant election campaign," says Ms Turei, "but that's their decision to do that. The Greens have been consistent on this issue for many years now, because we believe… it's a health issue."
But United Future Leader Peter Dunne, who has admitted smoking cannabis as a student, says the ACT party has finally lost the plot.
"It's just desperation, which has got no sense of coherence to it," says Mr Dunne.
"Policies on the one hand that let you take the law of justice into your own hands, on the other, drugs for all, then your deputy walks away.
"I don't see any consistency in that."
Labour has also attacked Dr Brash's reasoning for shifting his views.
"This is a sort of bizarre statement from Dr Brash, based on some strange notion that he appears to be the only one on the planet who believes that smoking marijuana has no effect on anybody," says Clayton Cosgrove.
"Good god, look at our young people, and look at the mental health issues we have in our prisons."
Political commentator Bryce Edwards told RadioLIVE this morning the party's alienating its support base and appears to be in trouble.
"For the last 15 years, ACT have increasingly gone after the officially conservative voters," says Mr Edwards. "This might actually be quite a problem for the typical ACT voter, and especially in Epsom."
All five of ACT's sitting MPs are bowing out of politics at this year's election.
3 News / RadioLIVE / NZN