Labour leader David Shearer says the proposed GCSB bill is "bad law" and would be repealed if the party was successful at next year's election.
However, he said the law would not be rolled back until an independent inquiry into New Zealand's intelligence services was carried out.
The comments follow a public meeting last night at which prominent academics and lawyers called for the GCSB bill to be canned.
Mr Shearer said the legislation - which he believed was likely to pass - would be left in place to govern the Government Communications Security Bureau while the inquiry was carried out.
"Otherwise you'd end up having a rogue agency operating without any legislation."