Opposition parties are furious police are refusing to release data to a gang researcher because he studied gangs by hanging out with them.
University of Canterbury sociologist Jarrod Gilbert, who spent 10 years living with gangs to produce his book Patched: The history of gangs in New Zealand, says police have cited his gang association for refusing to give him data on alcohol-related crime in Christchurch.
He has also released the contract police are making researchers sign, which gives them power to censor, amend or veto their work, or even blacklist them.
The Greens have come out strongly, saying it is an abuse of power and an outrage.
"This smacks of interference, and the minister must demand police stop trying to stymie academic freedom, or face accusations of political interference himself," said police spokesman David Clendon.
"I have no doubt that the real motivation behind these onerous contracts is political - to enhance the public perception of the police by manipulating research findings so they reflect positively on the police."
But Police Minister Michael Woodhouse isn't commenting, saying it's an operational matter.
"The way police go about it ... they have their own processes for information and data being released," a spokeswoman told NZ Newswire.
Police say their priority is a balance between privacy and academic freedom.
They will release information if it benefits them and the contracts ensure studies are "accurate, balanced and constructive", according to strategy deputy chief executive Mark Evans.
Labour's justice spokeswoman Jacinda Ardern says Dr Gilbert is owed both an explanation and apology.
The contract's powers were "extremely concerning", she said.
"What is at stake is the ability of researchers to carry out their work. Jarrod Gilbert's work is producing research with practical applications for our justice system."
The Tertiary Education Union says police withholding data is not an isolated case.
Government departments are wary of damaging headlines and this has led them to clamp down on public commentary from scientists, says national president Sandra Grey.