The Privacy Commissioner has criticised NZ Post for breaching the privacy of thousands of people in a wide-ranging public survey of personal data.
The 2009 survey, sent to 800,000 letterboxes and via email, asked a series of questions covering areas including income. The results were then on-sold to marketing companies.
The criticism comes as NZ Post is about to send out its latest survey.
Privacy Commissioner Marie Shroff commissioned two reports from privacy law and marketing experts.
She has concluded that the NZ Post survey was a systematic and large-scale breach of privacy principles.
Ms Shroff says one of her major concerns is that people are simply unaware that their private information is being sold.
"I think people need to be increasingly aware that to business, information about us has value. And when you add it all up together and if 800,000 people respond, that is a huge amount of detailed information about every household, every person."
NZ Post says its legal advice is that its surveys do not breach privacy laws.
Communications manager John Tulloch says part of NZ Post's business relates to direct marketing services and is enshrined in the State Owned Enterprises Act.
"Data collection for tailored marketing purposes is legitimate. The survey is very upfront about what its purpose is ... but it's also clear that it is voluntary."
Mr Tulloch says in the latest survey it has stated 11 times that it is voluntary.