The Salvation Army says moves by National and Labour to improve rental property quality mean little while landlords have "total power" over tenants.
Parliament is considering a bill in the name of Labour leader Andrew Little, which would require landlords to upgrade insulation and heating to a modern standard within one to five years.
It goes further than Government reforms passed into law last year, which would only require rentals with no insulation to be upgraded to a modern standard, and does not require heating to be installed.
Salvation Army social policy analyst Alan Johnson told a select committee today that he supported Labour's bill because it required higher standards for rentals than National's law changes.
But he said both parties' reforms of rental property laws were too narrow, especially given the legislation was 30 years old.
He said the reforms should have been broader, by addressing the lack of tenants' rights in New Zealand.
"It's all very well to talk about heating and insulation. But there's a bigger question around the fact that without decent rights, tenants have little power."
Landlords could still evict tenants with little reason, which made it hard for tenants to demand better quality properties, he said.
"I think it's important that we have legislation which ensures that tenants have secure tenure, that they're able to call the house they live in home, that they're able to get some of the benefits of home ownership offered."
The charity wants more secure forms of tenure, publicly-funded tenancy advocacy services, greater resourcing of compliance officers, and tougher sanctions for breaches of the law.
If Little's bill is passed into law, landlords would have to upgrade underfloor and ceiling insulation to 2008 standards within five years for existing leases, or within a year for new leases.
The changes in Little's bill would increase rents by an estimated $6 a week if the costs were spread over 20 years, the Labour Party estimated.
That estimate was based on costs for landlords of $3300 for retrofitting insulation, $2500 for installing a heatpump, and $500 for fixing draughts and ventilation.
The Government's bill required rentals that already had insulation to upgrade to 2001 standards, and those with no insulation to upgrade to 2008 standards.
Officials will be given new powers to investigate and prosecute landlords who break the law, and tenants will be able to take concerns to the Tenancy Tribunal without fear of being evicted.
The Government estimated its proposed changes would raise rents by $3.20 if spread over 20 years.
Housing Minister Nick Smith has said there was only a 5 per cent difference in heat loss between the 2001 and 2008 standards, and it did not make economic sense to force all landlords to upgrade to the higher standard.