It is up to those companies to make a judgement call about whether the information should be passed on to the spying agencies.
This approach will be preserved in the spying reforms being considered by Parliament.
However, Spark has joined Vodafone in calling for their discretion to be removed and for spies to make the call about whether information should be released.
Spark general manager of regulatory affairs John Wesley-Smith said MPs needed to provide certainty about what personal information intelligence agencies should be able to access without a warrant.
Any warrantless powers should be clearly defined, not delegated to private businesses, and have independent oversight, he said.
"In effect, the bill asks us to choose between protecting our customers' privacy and personal information or assisting our country's intelligence agencies with protecting New Zealand's security.
"We don't believe private organisations are best placed to make that decision. We don't think our customers want us making that decision.
"It's a decision that should rightly be taken by Parliament."
Wesley-Smith said Spark would comply with lawful requirements to provide information.
"But where there isn't a lawful requirement to do so we shouldn't be expected to."
He added: "[Spies] face the risk, and frankly we are seeing this risk more and more, that customer-facing organisations such as ourselves will decide that we are not interested in making these decisions and we will take policies that we are not going to provide information without a warrant."
National MP and committee chair Mark Mitchell said the committee was seeking advice from officials on the issue.
The reforms followed a broad-sweeping intelligence review by Sir Michael Cullen and Dame Patsy Reddy, released in March with 107 recommendations and proposing a single piece of legislation to cover both spying agencies.
The most controversial recommendation is to allow the GCSB to spy on New Zealanders without requiring a warrant to do so on the behalf of other parties.