Judith Collins says changes to the terrorism laws wouldn't have necessarily prevented Friday's attack.
An ISIS-inspired terrorist injured seven people at Countdown LynnMall on Friday.
Changes to terrorism suppression laws, which would criminalise planning and preparing a terrorism act, were already underway.
Jacinda Ardern is hoping to pass the changes as soon as possible.
The National Party Leader told Mike Hosking her party supports the legislation, but questions whether it would've been effective in this situation.
“That could have happened being monitored in a very similar way to what he was being monitored, but it probably wouldn’t have made a huge difference to him.”