Any cats that put a paw out of place in a protected area may be put down. That's if there's support for Auckland Council's pest management strategy which opens for consultation on Wednesday.
The Council proposes redefining the definition of a pest cat to include any that aren't microchipped or identifiable as being owned. Any cat caught in an "ecologically significant site" without a microchip could be put down.
Conservation campaigner Gareth Morgan says it "should have been done years ago".
"It's fantastic that they're doing it now," he told The AM Show on Wednesday.
"The issue really is cultural change for these owners to say 'look, have as many cats as you like - but keep them to yourself'.
"You can have companion cats - that's not what the argument is about. It's about having those and bringing more and more of New Zealand's natural wildlife into our cities."
Mr Morgan says this would give a massive boost to conservation efforts.
"In Wellington we're talking about bring kiwi back," he says.
"We just can't do this sort of stuff if these domestic animals are not reined in and confined."
Host Duncan Garner agrees, saying Mr Morgan's campaign changed his mind. He now wants a limit on cats.
"This is about changing our culture and our view in New Zealand to saving what we're spending millions on," he argues.
But the Council's plans have been attacked by cat-lovers, who say it's a revenue grab. Cat Society of New Zealand president Anne Batley-Burton believes the idea is "ridiculous".
"For a start the only reason they want to microchip cats is for revenue gathering, and it's a licence for the Council to kill strays," she told RadioLIVE, when the idea was proposed last year.
"It's a complete waste of ratepayers' money as well, all these rangers and people running around looking for stray cats."
She says stray cats aren't more likely to kill native animals than people's pets and the Cat Society is going to fight the Council on the issue.
Mr Morgan acknowledges it's controversial for many people.
"I don't think I've ever had as much hate mail and death threats on any topic as I have on domestic cats," he says.
"What is it about cats that drives people nuts?"