Health Minister Dr David Clark is the "very definition of a 'non-essential worker'" and has "humiliated" the Director-General of Health, Todd Muller says.
But Prime Minister Jacinda Ardern says the pair get along and rejects the portrayal of them as clashing.
Last week saw a border testing bungle where two women were released from managed isolation without a test and days later found they had COVID-19. Since then, it has emerged that 51 people were let out early without being tested.
Ardern and Dr Clark have previously said that leaving without a test is unacceptable and that they had been informed testing was occurring in facilities on day three and day 12 of guests' stay. Director-General of Health Dr Ashley Bloomfield has taken responsibility for gaps in protocols, something Dr Clark has been less than willing to also do.
Footage from Newshub on Wednesday showed Dr Clark telling media that Dr Bloomfield had taken the blame while the Director-General stood behind him quietly. It's since gone viral, with many condemning the Health Minister for deflecting responsibility.
After two political commentators lambasted the Health Minister on Thursday morning, Muller, the Leader of the Opposition, also let rip.
"David Clark’s treatment of Ashley Bloomfield is a disgrace. He humiliated a man we have grown to respect and trust during lockdown," Muller said in a statement.
"While Dr Bloomfield has fronted up day after day, Clark hasn’t even bothered to look at the quarantine arrangements that are so vital in protecting New Zealand from the virus.
"Clark is the very definition of a ‘non-essential worker’."
Muller has long been a critic of the Health Minister, last week calling for his head over the border mix-up. But Dr Clark has said it was an operational matter.
The National leader's Thursday statement said Dr Clark's "continued, bumbling presence defines the incompetence of the Labour Government". But Muller said he shouldn't be the one who accepts responsibility for the "furore", instead targeting Ardern.
"Did the Prime Minister know that Clark would be directing all blame on Dr Bloomfield?
"Jacinda Ardern is happy to take centre-stage during lockdown briefings but as soon as there's bad news, she is nowhere to be seen.
"For Ardern, when things go wrong, the buck stops with the frontline workers, never her Ministers, never herself."
Ardern could be heard on The Rock on Thursday morning defending the Health Minister and Director-General of Health.
The viral video had many commenting that the pair seemed to now have a frosty relationship. National's Health spokesperson Michael Woodhouse also said on Wednesday there appeared to have been a breakdown in relations.
"We've seen from the body language over the last couple of weeks that the relationship between the Minister of Health and the Director-General has deteriorated."
Asked what the chances are that Dr Clark would send Dr Bloomfield a Christmas card later this year, Ardern said the pair are "absolutely fine".
"Both of them, I think, feel like they have both been really let down. I have seen some of that portrayal. I don't think it's particularly fair. They get on well."
Dr Clark previously came under pressure to resign after breaching New Zealand's lockdown rules. After driving to the beach with his family when Kiwis weren't meant to be going out for non-essential purposes, Dr Clark was stripped of his Associate Finance Minister role and demoted in the Cabinet rankings. Ardern said she would have sacked him as Health Minister if the country hadn't been in the middle of a health crisis.