The Privacy Commission has joined calls for further investigation into proposed new spying powers.
Commissioner Marie Shroff says the Law Commission should be asked to examine legislation and oversight of intelligence agencies.
The Government is proposing the Government Communications Security Bureau Amendment Bill to make it legal for the agency to spy on New Zealanders on behalf of other law enforcement bodies.
It says it is necessary to clarify the law after the GCSB was found to be illegally intercepting communications.
But the bill has met opposition, including from the Law Society and the Human Rights Commission.
Now the Privacy Commission has joined the chorus, saying the GCSB's powers must be "demonstrably necessary and justified".
It says the bill is not specific enough about what the oversight mechanism is for GCSB's activities on behalf of other agencies.
There are also questions over the protection of privacy.
The commission says the bill should be delayed until these issues have been examined.
"It is worth investing in some additional consideration to ensure that we have the soundest model possible," the commission says in a submission to Parliament.
However, the report notes that updating the law is necessary "in our complex digital world, so that GCSB can keep pace with new threats to New Zealand, both in the traditional intelligence sphere and in the area of cybersecurity".