National Party leader Simon Bridges says this week's behaviour by the government was "contemptible" in bringing in the police over the Budget data breach.
Mr Bridges has spoken to media after Treasury said this morning that the Budget breach wasn't unlawful.
Watch Simon Bridges' full press conference here:
He said Treasury knew since Tuesday what had happened and were covering up their "incompetence" and that Treasury Secretary Gabriel Makhlouf "must resign".
He also said Finance Minister Grant Robertson had played politics throughout should also resign as he did not have the "moral authority" to deliver the Budget today.
He denied having acted unethically, despite being challenged over his party's conduct.
Mr Bridges said National "came across" the Budget material by doing a simple internet search on the Treasury website.
It was National's duty to access the information, he said.
"It was the right thing to do. It shows the incompetence of the government and it showed that this Wellbeing Budget is just glossy pictures."
Treasury has confirmed that a feature in its website search tool was exploited by an unknown person or persons, but police have concluded this did not break the law.
The investigation found one of the IP addresses involved in the searches belonged to the Parliamentary Service.
Yesterday, Mr Robertson and Mr Bridges were locked in a stand-off over the leaking of Budget information.
Just hours before delivering the Budget the Finance Minister issued a statement placing the blame on the Treasury for the fall out resulting from the Budget leak.
In a statement, Grant Robertson said he was very disappointed confidential Budget information was able to be accessed.
He said it was disappointing that the Treasury did not seek to find more information as to how it had happened before referring the matter to the police.
Following Mr Bridges' press conferecne and Mr Robertson's statement, Treasury saidt has nothing to add.
It also said it had no comment on Mr Bridges revealing the party conducted a simple search, rather than a hack of the Treasury website.