The Auckland Property Investors' Association (APIA) is warning costs imposed on home-owners by upcoming law changes will flow on to tenants.
The first part of a Government bill ensuring there are working smoke alarms in all rental properties and insulation in social housing comes into force on Friday.
But APIA vice-president Peter Lewis warns most landlords simply can't afford to fund the upgrades, which will lead to rent increases.
"Most landlords are generally not further up the economic tree than their own tenants tend to be. So we are likely to see an increase in rents when this sort of obligations is put on most landlords, simply because they can't afford to do it without some recompense."
The new standards could also reduce rental supply because owners who would have rented homes for short periods will now find it more economical to leave them empty, Mr Lewis claims.
"It's now going to be a bit of a problem if you just want to let your house for a year, 18 month while you're away working or on a long holiday. But that's one of the unintended consequences that always come up in this sort of legislation."
Mr Lewis says it's unfair rental properties are having higher standards enforced on them when owner-occupied properties are not.
He believes there should be one rule for all, in the same way all cars must have a Warrant of Fitness.
"It doesn’t make sense that owner-occupiers are far more able to resist the rigours of unsatisfactory houses than tenants are. But I mean, that's the law at the moment that we have to live with."
Mandatory insulation standards for private rental properties do not come into force until July 2019.