ACT leader David Seymour says Labour is acting in a Trumpian manner by spreading what he calls "misinformation" about its policies.
"That's what Donald Trump does," Seymour said in Wellington on Tuesday morning.
"He tries to bamboozle people with his alternative truths and mistruths. What happens is people lose faith in their institutions. I ask Labour, if they want to criticise our policies, we have lots of policies they can criticise without them criticising policies we don't have."
Asked what he made about the comparison to Trump, Hipkins said it was "absolute nonsense".
Seymour made the comment in response to a question about Labour posting on social media that a National-ACT coalition would cut fees-free for first-year tertiary students and also add interest back onto current student loans.
Both National and ACT have said they don't have a policy to reintroduce interest to student loans. National is committed to keeping fees-free, though ACT wants to dump it.
Labour removed the claim last week.
"It is shocking, isn't it," Seymour said.
"They aren't running on their record, we understand that. They are not running on our record. They are running on things we haven't even said. What I would say to Labour, is we are lucky to live in a democracy, but a democracy depends on truth. When a political party deliberately goes out and spreads misinformation, that erodes people's trust in our democracy."
Speaking from Wainuiomata, Hipkins said he believed Labour was running an honest campaign.
On Labour's social media post, Hipkins called it "human error" and "it won't happen again."
Labour has also been saying that National's tax cuts are unaffordable as its proposed revenue-gathering measures won't bring in as much money as it plans.
"They will have to scrap them or make even deeper cuts to public services like health and education," finance spokesperson Grant Robertson said.
Hipkins was asked if it's fair to make the claim that National could cut health and education services when National has excluded the likes of Te Whatu Ora, the Ministry of Education and Corrections from having to deliver efficiency dividends.
He replied by saying that as National's tax numbers "simply don't add up", the party would have to cut into public services or borrow more money.
"Their tax plans just continue to fall apart. Really, the National Party needs to say how they are going to fund these things if they are not going to cut into funding for public services."
Hipkins also came to the press conference armed with more examples of National's "negative campaigning" about him and Robertson. They included a social media post saying, "even eight-year-olds know better than Hipkins".
"I am glad they are not going personal with any of their advertising campaigns," Hipkins said.
On Monday, National took offence at a Council of Trade Unions advertisement targeting leader Christopher Luxon that it claimed Labour was involved in.
The Labour leader hit out at National for being "thin-skinned" and said he was frequently attacked by National and right-wing groups.