"This is not, and never will be, about wholesale spying on New Zealanders," Key told parliament.
"There are threats our government needs to protect New Zealanders from, those threats are real and ever-present and we underestimate them at our peril."
The push to change the law came after it emerged last year that the GCSB illegally spied on Internet tycoon Kim Dotcom before armed police raided his Auckland mansion as part of a US-led probe into online piracy.
At the time Key publicly apologised to Dotcom, who is a New Zealand resident and should have been off-limits to the GCSB under legislation preventing it from snooping on locals.
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