Prime Minister John Key gave an assurance yesterday that New Zealand's spies in the SIS and GCSB could not gather information about a person from various databases and then apply for a warrant after the fact.
He made his comments at his post cabinet press conference amid groups such as the Law Society expressing concerns about a bill that expands spy powers for agents at the Government Communications Security Bureau and another bill that allows the Government to expand the types of organisations that must co-operate with spy agencies for interception purposes.
"They don't have the authority to simply put in techniques to exfiltrate information and then backfill that with legal justification for doing so via warrants," Mr Key said.
"In other words they can only access information when they are legally entitled to do so, and they can't circumvent that process by gathering information upfront.
They have to do that reactively, not proactively."
Mr Key has previously said New Zealand agents acted lawfully but is usually short on detail.
Recent leaks to the Guardian newspaper in Britain suggest that British and American spy agencies collect and trawl through vast amounts of data before applying for legal search warrants.
Mr Key acknowledged yesterday he was still working on getting enough support for the GCSB Act after United Future leader Peter Dunne said at the weekend his support was not guaranteed.
Mr Key is hoping to get New Zealand First leader Winston Peters on board and said he was open to amendments to the bill.
Mr Key said Mr Peters had been familiar with information relating to national security as a former Minister of Foreign Affairs.
"He highly values it. He takes national security seriously and I think on the back of that he will take a very close look at this legislation."
The bill gives the GCSB lawful authority to spy on New Zealanders when helping other Government agencies duly authorised to intercept communications, which the GCSB has been doing for years possibly unlawfully, and when undertaking cyber-security functions.
Mr Key, who is minister responsible for both the GSCB and Security Intelligence Service, said the bill was not being rushed through but needed to passed "reasonably rapidly" because New Zealand was more vulnerable with GCSB assistance to Defence, the SIS and Police suspended.
"That puts New Zealand in my view in a slightly more vulnerable position and it needs to be fixed up."
In the event of the bill not having the numbers to pass, the activities that had been undertaken against legitimate targets by the GCSB in helping agencies that had had warrants to do so would have to be done by the agencies at significant cost.
"It's not a question of whether surveillance work is undertaken against legitimate targets for which there is warranted authority, it's about who undertakes that. In my view the right place is GCSB."
The Intelligence and Security Committee will begin hearing some of the 121 submissions on the bill next week.
The committee is required to report back to the House by July 26.