The Greens will push for permanent rent control and a national landlord watchdog if they hold the balance of power in the next parliament.

In a new proposal, the minor party wants to fine landlords thousands of dollars if they breach strict rules including minimum kitchen and bathroom sizes and rent hikes of no more than 2 per cent every two years.

The policy would be difficult to implement since it exceeds the legal powers of the federal government and would require major concessions from states and territories.

But the framing reflects the minor party's belief it can woo renters squeezed by a historically tight rental market.

It also puts the Greens further at odds with Labor's argument that housing supply is at the root of affordability problems, given considerable international evidence that rent controls dampen supply.

Greens housing spokesperson Max Chandler-Mather said the status quo was "stacked against renters" and meant landlords "never do basic repairs".

"Across this country, there are 7 million renters who are powerless in their own home … We desperately need a national body with teeth to fight in their corner."

States asked to hand over powers for cash

The Greens propose national minimum rental standards for heating and cooling, bathroom and kitchen size, security, ventilation and mould.

Variations on those standards already exist at state and territory level, and the federal government struck a national agreement last year to strengthen and harmonise them.

But the Greens want states and territories to go further by giving tenants a guaranteed right to lease renewal and a "presumed" right to five-year leases, while also preventing landlords from evicting tenants because they want to sell their property.

They also seek agreement to a two-year rent freeze — something several state and territory governments have ruled out — followed by a perpetual rent increase cap.

Under that cap, new or renovated rentals would start at the median for their area and property type, effectively locking in the inner-city rent premium even if new housing is built.

To get states and territories onside, the Greens propose the federal government offer them housing grants of a combined $2.5 billion a year.

For that price, they would also be expected to hand over their constitutional powers to make laws for renters, so that the federal government could set up its own watchdog to enforce the rules and pursue landlords over bond disputes.

The watchdog could impose fines of up to $15,650 on landlords, or up to $78,250 on property agencies.

A Greens spokesperson said the watchdog could overrule state and territory dispute tribunals, but that landlords could appeal to those tribunals.

Economist says rent controls restrict supply

Peter Tulip of the Centre for Independent Studies said the policy was "well-intentioned" but would backfire.

"It's pretty obvious that the rapid increases in rents are hurting people, and you can understand the instinct to mitigate that and stop it getting any worse," he said.

"But the problem is rising rents reflect the housing shortage, and rent controls make that shortage worse."

Surveys collating decades of research on rent controls show a strong consensus that they constrain supply, erode rental quality and do not improve equity.

"We have many, many examples of rent controls being imposed all around the world and they've repeatedly backfired," Mr Tulip said.

Greens, Labor at odds over cause of crisis

The Greens' approach contrasts with the federal government, which identifies restrictive planning laws as the primary culprit of affordability woes, a view echoed by Labor governments in NSW and Victoria.

It has set a target for 1.2 million new homes in the next five years, offering bonuses to encourage states and territories to reform planning laws.

Mr Tulip praised the target and said it "should be achievable," but said not enough was being done to meet it.

"Instead of aggressively pursuing those targets, the federal government has been wasting its time and effort on symbolic policies that do very little for affordability."

He cited the government's Help To Buy scheme, stalled in the Senate, which would assist 40,000 first home buyers.

"That doesn't even amount to a rounding error on 1.2 million."

As well as reforming planning laws, Mr Tulip said rental insecurity could be addressed by reducing the tax paid by large-scale housing investors.

"We've got the wrong landlords. Our rental stock is owned by mum and dad investors who churn at an enormous rate," he said.

"We'd have much more secure rentals if, like in parts of Europe and the US, we allowed large corporations to own our renting stock, but our progressive land tax system makes it prohibitively costly.

"Single-property landlords essentially don't pay land tax, but any investor large enough to own a block of flats will pay 2 per cent tax. That is going to eat up a huge share of the rental income, so it's not economic."

The Greens argue to the contrary that property tax breaks for investors, in particular negative gearing and the capital gains tax discount, have "rigged" the housing market.

Last week, Greens leader Adam Bandt used a National Press Club to accuse the government of "turbocharging the increasing cost of housing by handing $176 billion in tax handouts to wealthy property investors", renewing calls to scrap negative gearing.

Research by Mr Tulip and by the Grattan Institute suggests negative gearing reform would make at best a modest difference to house prices.

Housing election takes shape

On Sunday, Coalition assistant housing spokesperson Andrew Bragg accused the government of constraining housing supply by "letting the CFMEU run the migration program" in restricting the inflow of construction workers.

He also said the Coalition would consider ways to "hit the states and the councils in whichever way we can" to reform planning laws, such as by withholding payments.

The Coalition's only confirmed housing policy for the next election would boost demand by giving first home buyers access to their superannuation.

On the ABC's Insiders, Senator Bragg denied this would push up prices, claiming it would make "minuscule or nil" difference.