The Environmental Protection Agency (EPA) should urgently review the safety of a common ingredient in many weedkillers, the Green Party says.
The party wants councils to stop using weedkillers containing glyphosate in parks, playgrounds and street verges. It is launching its "spray-free parks and streets" campaign at Onepoto Domain in Auckland today.
A World Health Organisation committee last year stated that glyphosate was probably carcinogenic.
However, New Zealand's EPA said current international opinion was that the chemical was safe to be used as a weedkiller.
Green MP Steffan Browning said the agency needs to re-assess the safety of glyphosate, the active ingredient in weedkillers like Roundup.
"Our survey of councils shows thousands of litres of glyphosate are used on berms, playgrounds and parks every year, putting people at risk from a probable carcinogen," Mr Browning said.
He said there were safe alternatives that could be used to kill weeds, such as hot water, weed trimmers and mulching.
Many cities overseas, including Paris, Chicago and Barcelona, had stopped using glyphosate products in public areas, Mr Browning said.
But Auckland Council's chief operating officer Dean Kimpton said the cost of not using glyphosate would be prohibitive.
"Hot water or steam is two to three times more expensive than glyphosate in a similar application. If you go to the mechanical or manual form of weed control, those costs vary significantly and can be far greater as well."
Mr Kimpton said the council was comfortable with the authority's advice.