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.