Prime Minister Jacinda Ardern says it was "unfair" of ACT leader David Seymour to suggest pre-departure testing of passengers from Sydney could have prevented the current lockdown.
The Government confirmed last month that the Delta outbreak in New Zealand was linked to an arrival in managed isolation and quarantine (MIQ) from New South Wales, which is raising questions about how the virus got in.
New Zealand closed the quarantine-free trans-Tasman bubble on July 23 after daily case numbers began rapidly increasing in New South Wales, and popping up in other parts of Australia.
Each passenger had requirements on them before they entered New Zealand in the one-week window the Government gave people to return home.
Travellers from outside of Victoria and New South Wales were able to get on flights and not go through managed isolation, but had to provide evidence of a negative pre-departure test.
Those in New South Wales did not require a pre-departure test, but had to spend 14 days in managed isolation upon their return, which involved a test on arrival and subsequent tests.
Ardern told reporters on Monday the Ministry of Health did not recommend pre-departure testing of passengers from Sydney.
"The view of the Health team was to allow them to come back and test them on arrival. So that was the advice that we were given," she said at her post-Cabinet press conference.
Seymour asked Ardern in Parliament on Tuesday if she regretted that decision, "just as Auckland enters its fourth week of lockdown".
"There is no way anyone in this House or anyone in New Zealand would want to be in the place we are with people in lockdown right now, of course, but it is overly simplistic to imply that had that one thing been in place, this wouldn't have happened," Ardern said.
"I don't think that's fear, particularly given what I recall of the timeline of when we believe this person became infected. I just don't think it's a fair summation."
Ardern said pre-departure testing is just one layer of defence.
"It is not perfect, absolutely not, because you go and get a test 72 hours before you depart, you still have a possibility of being infected in those 72 hours, or indeed, in your transit to New Zealand, and we've seen multiple situations where people have been infected with COVID-19 and often what is very long journeys back to New Zealand.
"So it is another layer, it is not a perfect layer, we do not rely on it. That is why we test people when they arrive as well, and we continue to test them throughout the duration of their stay."
Seymour said his claim was not overly simplistic.
"The truth is it was a simple step that could have prevented this lockdown," he said.
"The Government said today that it was more risky for someone in Sydney to get a test and risk getting COVID than it was to have a test.
"By that logic, the Prime Minister is saying there's more chance of catching COVID going to get a test, than a test catching COVID."
