Porirua Mayor Nick Leggett says Labour leader Andrew Little's plan to upgrade all rental properties has some large gaps.
Leggett - who Little described as "right-wing" in a war of words last week - criticised the absence of enforcement measures in Little's Healthy Homes Guarantee Bill.
Speaking in front of a select committee this morning, the mayor said he was "very supportive" of the intent of the bill.
Porirua had some of the worst rates of child hospitalisations in the country, most of which were related to substandard housing.
However, the legislation was "silent on enforcement", he said.
"That's the key for us. It's actually making something happen.
"You can dream up legislation that paints blue skies and rainbows as much as you like, but unless it brings change and it tasks responsibility to an authority or institution and makes them responsible and gives them resources ..."
"Because local government, we love mandates. But what we love even more than that are funded mandates."
Assessing all the city's rental properties would take two years and require eight full-time staff, he said.
This would cost roughly $1.2 million a year, or 2 per cent of Porirua's rating take.
"We're not saying don't do it. We're saying you're going to have to think about who's going to pay for that."
Local government, we love mandates. But what we love even more than that are funded mandates.
The council's chief executive Wendy Walker said a team of eight staff would be more than the council's entire existing regulatory team for food, alcohol, and resource consents.
Labour's housing spokesman Phil Twyford said he took issue with Leggett's assertion that the bill was "silent" on enforcement.
It required landlords by law to certify that their properties met minimum standards, he said.
"If they are found to be in breach of that then they face a hefty fine and compensation to the tenant. That's not [silent on] enforcement."
Little attended the committee hearing, though he missed most of the Porirua Mayor's submission.
If his bill is passed into law, landlords will have to upgrade underfloor and ceiling insulation to 2008 standards within five years for existing leases, or within a year for new leases.
It goes further than recent Government reforms, which require rentals with no insulation to upgrade to 2008 standards by July 2019.
Leggett, a former Labour Party member, is running for the Wellington mayoralty in direct competition with the Labour-endorsed candidate Justin Lester.
Last week, Little said Leggett's campaign was being funded by right-wingers, and he blocked a Labour MP from speaking at an event at which Leggett was speaking.