The Green Party is accusing the police of misleading the public about part of the investigation into the Government's surveillance of internet mogul Kim Dotcom.
The police announced in August they would not lay charges against anyone at the Government Communications Security Bureau.
They said their findings were independently reviewed by senior barrister Kristy McDonald QC.
However, in emails to Mr Dotcom's lawyer, police say Ms McDonald actually just provided oversight of the inquiry.
Furthermore, the Green Party says Ms McDonald cannot be independent as she is also representing the police in another case against Mr Dotcom.
Green Party co-leader Russel Norman told Morning Report there have been problems with police decisions in cases that have a political dimension.
"That process whereby the police make the decision I think really has come under the spotlight, with the John Banks case where the police decided not to prosecute and then the courts, as the result of a private prosecution, decided to go ahead and now this case where the police decided not to prosecute," he said.
The Independent Police Conduct Authority confirmed on Thursday it had launched its own inquiry into how police handled complaints about the GCSB, including Ms McDonald's involvement.