Finance Minister Grant Robertson has called on the National Party to stop releasing any Budget-related material as the Treasury says it has been hacked.
But National leader Simon Bridges has fired back, saying his party has acted "entirely appropriately".
He said Robertson "falsely smeared us [National] to cover up his and The Treasury's incompetence".
"When what has occurred is revealed, he will need to resign."
This evening, the Treasury revealed it was confident the information released by the National Party in a series of press releases today came from hacked information.
"Following this morning's media reports of a potential leak of Budget information, the Treasury has gathered sufficient evidence to indicate that its systems have been deliberately and systematically hacked," the Treasury said in a statement this evening.
"The Treasury has referred the matter to the police on the advice of the National Cyber Security Centre."
The hacking of the Treasury website would be a major issue for the Government and Bridges digging his heels in on the eve of the Budget's release will be hugely problematic for the Government.
Robertson said he had contacted National, asking Bridges not to release any more information – "given that the Treasury said they have sufficient evidence that indicates the material is a result of a systematic hack and is now subject to a police investigation."
He said the matter was "extremely serious" and now was in the hands of the police.
"What New Zealanders care about are the issues that will be dealt with in the Wellbeing Budget on Thursday, and that is what we continue to be focused on."
But speaking to Magic Talk earlier tonight, Bridges said the way National got the information was "lawful".
"It was the Beehive and the Treasury that is in a frenzy right now – they are leaking like a sieve and it shows a pretty shambolic Government."
He had previously refused to say if National had acquired the information from a leak.
Asked if he knew where the figures came from, Bridges confirmed he did, in fact, know.
But he refused to say where and how he got the information.
"Who knows, we may get a bit more."
But he did say he could confirm it was "lawful".
"There is no funny business, if you want to put it that way."
Earlier today the Herald found the Treasury website had holding pages on its website with headings for the same 19 vote overviews that National has released details off.
They were dated May 30 and locked so access was blocked.
All 19 have now been taken off the website. About 21 other overview pages - including education and welfare - had not been put up at all and no details from those have been released.
However other Budget 2019 pages were up - including the overall estimates.