Opposition parties say changes negotiated by Peter Dunne to a bill on the country's electronic spy agency only mask a dangerous and deeply flawed piece of legislation.
The independent MP will give the Government the one vote it needs to pass a bill allowing the Government Communications Security Bureau (GCSB ) to spy on New Zealanders.
Changes negotiated by Mr Dunne include making it harder to allow the GCSB to assist agencies other than the police, Defence Force or the Security Intelligence Service (SIS). As part of the changes, the Inspector-General will be notified when there is a warrant relating to a New Zealander.
The bureau will have to report annually on the number of times it assists other agencies and on the number of warrants and authorisations issued. There will be an independent review of the GCSB and the SIS in 2015, and every five to seven years after that.
Mr Dunne and Prime Minister John Key say the changes bring greater oversight and transparency. Mr Key says the bill will specify what information cannot be looked at, such as medical records, which will be excluded from warrants.
However, Labour and the Greens say the amendments are cosmetic and do little fundamentally to protect New Zealanders' private information.
Labour leader David Shearer says the changes are superficial. "What we've got is a piece of patched up legislation that Peter Dunne has agreed to and an inquiry some time in the future, and that's not good enough."
Green Party co-leader Russel Norman says none of the changes will stop the GCSB spying on New Zealanders. "It's remarkable that Peter Dunne has rolled on this bill given that he himself has said that he wanted to protect the content of his emails from the Prime Minister - something that I supported his right to do."
Mr Key has said that he wants to build broader political support, but with Labour and the Greens effectively ruled out he has only New Zealand First, which has conditions of its own.
New Zealand First leader Winston Peters told Morning Report that Mr Dunne had sold out out in deciding to support the legislation and changes to the bill are illusory.
"The so-called parliamentary review is as to finance only, it's not to do with what they're actually doing. The panel is not independent.
"More importantly, you're taking an agency that wasn't allowed to spy on New Zealanders and giving them a significant opportunity to begin spying on New Zealanders and then justify an expansion of that. That's what New Zealanders will be alarmed at."