The Green Party has lodged a complaint with the Ombudsman following the outcome of an inquiry into the leaking of a report into the Government's spy agency.
The Greens claim that inquiry head David Henry had no authority to access the email account log of independent MP Peter Dunne.
Mr Henry was unable to identify who was responsible for the leak, but said Mr Dunne did not fully co-operate with requests to provide his email correspondence with the reporter to whom the report was leaked. He found Mr Dunne exchanged 86 emails with the reporter in the weeks leading up to the leak.
Green Party co-leader Russel Norman said on Monday that David Henry should have sought permission from Peter Dunne before accessing a record of his email account.
Dr Norman said the parliamentary email server belongs to Parliament, not the executive.
"This is a fundamental breach of the constraints on the executive; so in our system of government the executive and the Parliament and the judiciary are all separate."
Dr Norman said the Prime Minister's Office needs to explain how it was lawful for Mr Henry to access an MP's email logs.
The Prime Minister's Office said its Chief of Staff can ask Parliamentary Services for a report on specific emails sent or received by ministerial staff, but not without the MP's permission.
Prime Minister John Key told reporters on Monday there was nothing unlawful with the inquiry into the leaking of the report. Mr Key said his ministers knew that David Henry would be checking email logs in the investigation.
"My office made it very clear I expected people to comply. When people swore the Oath of Allegiance, they understood exactly what was expected of them and the terms of conditions spelled out absolutely in plain English what was going to happen and what information was going to be looked at, and that included email traffic."