The Greens have lodged a formal complaint against the Sensible Sentencing Trust, accusing the lobby group of impersonating the party with its latest election attack ads.
The billboard ads were created by the Campaign Company, owned by Taxpayers' Union boss Jordan Williams.
They feature Green co-leaders Chlöe Swarbrick and Marama Davidson and Labour leader Chris Hipkins alongside the text "BACKING THE GANGS" above the Greens' campaign slogan "for all of us".
Swarbrick called the ads an "entirely new low" and called on Prime Minister Christopher Luxon to condemn the "despicable downgrading of democracy".
The Greens have complained to the Advertising Standards Authority (ASA).
JC Decaux, the media company that owns the billboards, told RNZ it had paused the ads, while it reviewed the concerns raised.
The party said the SST was a Taxpayers' Union "astroturf group" - that is, a fake grassroots organisation supporting the same cause.
SST spokesperson Louise Parsons denied that - "We certainly aren't TPU at all" - but confirmed the involvement of Williams' company.
"We just want to try and get our message across, and that's what we've done. We're not going to make any apologies for that at all."
The ads were meant to warn voters against a Labour-led coalition, referring to a "spike" in crime under the previous Labour government, she said.
"We are intent on not allowing them back in to do it again," she said. "We're trying to avoid further victims."
The SST was also behind last year's 'Defund the police' billboards resembling Green Party campaign hoardings.
The Green Party complained to the ASA about those too.
In that case, the ASA upheld the complaints in part, saying the advertiser's identity must be clearer to avoid confusion. It did not uphold complaints that the ads caused harm or offence.
A Taxpayers' Union spokesperson said it did not create the latest ads.
"For a party demanding a clean campaign, even getting their facts right would be a good start," they said.
The SST and the Taxpayers' Union run a shared website called 'We can't afford Labour'.
Asked for his response to Swarbrick's comments, a spokesperson for Luxon referred RNZ to the organisation responsible for the ads.
A Labour Party spokesperson said: "While this ad is nasty and untrue, we're unlikely to make a complaint against it."
The ads follow the saga involving Labour, Greens and Te Pāti Māori candidates campaigning with gang members.
Labour candidate Kerrin Leoni resigned, after Hipkins took a hard line on the matter, but the Greens and Te Pāti Māori have been unapologetic, saying they would not turn their back on gang whānau.
