National says meetings of top ministers should not be done through video link service Zoom, given security concerns.
Reports have emerged that flaws within Zoom's security system could give hackers access to their target's microphone and camera.
There are also concerns that changes in Zoom's terms and conditions allow the company to keep chat messages and files exchanged in meetings.
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National's Government Communications Security Bureau and Security Intelligence Service spokesman Gerry Brownlee said Prime Minister Jacinda Ardern has serious questions to answer about why Cabinet continues to use Zoom.
He wants Cabinet to switch to an alternative platform which is safer.
"It's important Cabinet follows the rules that every other New Zealander is around distancing, but there has to be a better way than over a platform that is vulnerable to hacking," he said.
"Cabinet needs to be able to have robust discussions in a protected environment. It's where decisions at the highest level are made for New Zealanders."
Ardern earlier this week said the video link service had been vetted by security agencies.
She said it had been given the green light for conversations up to "Restricted" level - or below the Secret and Top Secret levels in the GCSB's official guidelines.
But she did say Cabinet would not discuss certain agenda items on Zoom.
"We are acting cautiously in line with the advice that we've had from officials."
But Brownlee said this was not good enough and Zoom was not appropriate to be used in Cabinet at all.
"The moment she [Ardern] knew there were vulnerabilities she should have looked for another platform," he said.
A GCSB spokesman said: "The Bureau is aware of commentary overnight relating to the security of the Zoom platform and will consider if additional guidance around its use is required."
Security expert Daniel Ayers has similar concerns.
He questioned why Zoom was being used when safer alternatives used full end-to-end encryption.
A Zoom spokesperson has said that it takes its users' privacy, security, and trust extremely seriously.
"During the Covid-19 pandemic, we are working around the clock to ensure that hospitals, universities, schools and other businesses across the world can stay connected and operational."