Cracking down on offshore buyers of New Zealand property is justified even if they are buying just one in 20 homes, the Labour Party says.
Land Information New Zealand is expected to release property data in the next fortnight which will provide a detailed record of the scale of foreign investment in the housing market for the first time.
The release of the data, which has been collected since October, is likely to reignite the political debate on whether non-resident investors are pushing up house prices.
Prime Minister John Key says that the best response to high levels of sales to overseas buyers would be a land tax on non-residents. But he will not say what percentage of sales to non-residents would trigger such a policy.
Labour's housing spokesman Phil Twyford said he was sceptical about the property data, because the Government could release it selectively.
But he said that he would want the Government to step in even if non-resident purchases were revealed to be at the modest end of the scale - such as 5 per cent of all sales.
There were 32,000 houses sold in Auckland in the year to March, according to the Real Estate Institute of New Zealand. If 5 per cent of them were sold to non-residents, that would amount to 1600 homes.
Mr Twyford said that in an overheated housing market, that was too many.
His party wants the Government to go further than a land tax by banning non-resident buyers altogether, unless they were investing in new builds.
The new property data was scheduled for release this month, but the deadline has been pushed back to give officials more time to analyse it.
A spokesman for Land Information Minister Louise Upston said the data would show whether a house was sold to a person with a New Zealand tax number or an overseas tax number, and whether they would be living in the house.
It was not yet known whether the data would reveal which country the buyer came from.