The contest has seen both major parties reach for the dark arts already, with Labour eager for a third term from the October 14 poll, and centre-right opposition National just as keen to prevent that.
National campaign chair Chris Bishop said the front page NZ Herald ad was "nasty" and showed Labour's shift away from Jacinda Ardern's relentlessly positive style.
"'Be kind' has truly become 'be nasty' under Chris Hipkins and his union elite buddies," Mr Bishop said, referencing one of Dame Jacinda's slogans.
Mr Bishop said Labour had launched the "most negative campaign in history", predicting six weeks of "disgraceful" attacks on Mr Luxon ahead.
"We are not going to engage in the nasty, personal, petty, vindictive politics that the union movement and the Labour Party are going to engage in," he said.
Appearing at a press conference in Wellington an hour after Mr Bishop's comments, Mr Hipkins said National already were doing so - and brought the evidence to prove it.
The Labour leader brought print-outs of National advertisements lampooning himself and other party leaders published in recent months.
"They have been running attack ads against me and against the government since the day I took on the job," he said.
Mr Hipkins' message for National? Toughen up.
"If Chris Luxon and the National Party are going to do that every time someone critiques or criticises what they're doing they probably need to rethink whether or not they're cut out to be in government," he said.
"It's incredibly thin-skinned."
National has a narrow lead in recent polling but the contest is tight, with minor party support and coalition-building likely to confirm the outcome.
Last week after a poor poll for Labour, Mr Hipkins pledged to "fight back" against National, which he said hadn't endured enough scrutiny.
The NZ Council of Trade Unions (NZCTU) advertisement is part of a broader campaign including billboards and television ads, and a website: outoftouch.nz.
The NZCTU is primarily concerned with National's pledge to abolish fair pay agreements, similar to Australia's industry-wide bargaining.
"National Leader Christopher Luxon is out of touch and focused on the wealthiest few. He calls people bottom feeders," the video ad begins.
"He wants to scrap fair pay agreements for bus drivers and cleaners. He'll make you pay for prescriptions and he plans to give billions in tax cuts to landlords, putting funding for schools and hospitals at risk.
"Luxon isn't the right leader in a cost of living crisis because he doesn't understand life for everyday Kiwis.
"Christopher Luxon. Out of touch. Too much risk."
Mr Luxon spent 16 years living abroad building his career before returning to work as an Air New Zealand executive in 2011 and entering parliament in 2020.
