Phil Twyford says Auckland owes a real estate employee who leaked data about thousands of real estate deals a "debt of gratitude".
The Labour Party housing spokesman said this morning the Government did not want Aucklanders to know what was happening with the city's property market.
The data covered almost 4000 house sales by one unidentified firm from February to April.
Real estate figures published in the Weekend Herald suggested people of Chinese descent accounted for 39.5 per cent of transactions in the city in that period.
Barfoot & Thompson fired an employee after the data was leaked.
This morning, Mr Twyford told TV One the employee's sacking was disappointing but he did not regret helping release the information.
"I absolutely stand by releasing that data," he said. "New Zealand is being sold off under our feet."
He said "offshore speculators" were running rampant in Auckland's real estate market.
Mr Twyford said he would not reveal his "contacts or communications" with the person who approached him and passed on the information.
"The reason we put this leaked sales data into the public domain is that the Government has refused to collect the information and refused to make it public. And I believe people have a right to know what's going on," he told NZME News Service.
He said banning offshore buyers from snapping up Auckland properties would not in itself solve the housing crisis."It has a number of causes.
Addressing one issue [won't] fix the entire problem but it's plain silly for some people to suggest that because a given policy solution like banning foreign buyers won't instantly fix the problem that therefore we shouldn't talk about it. We need bold reform on a number of fronts."