A union representing public sector workers has slammed the Housing Minister for referring to the "kids at Treasury" for the slash in the impact of KiwiBuild.
Analysis in December predicted the policy would bring in $5.4 billion in additional residential investment. But in this week's Budget, that figure changed to $2.5 billion.
"I don't agree with Treasury's numbers. They've made some very questionable assumptions," Phil Twyford told Newshub on Friday.
"Some of these kids in Treasury are fresh out of university, and they are completely disconnected from reality".
Public Service Association national secretary Glenn Barclay says the minister needs to be careful with his words.
"To personalise this about the public servants concerned is disappointing," he told Newshub.
Mr Barclay says ministers need a better understanding of what public servants do.
"It's their job to provide them with free and frank advice, and they need to respect that."
Ex-Finance Minister Steven Joyce, a former National MP, said Mr Twyford's barb was "reasonably high on the arrogance scale" and National housing spokeswoman Judith Collins said Mr Twyford "arrogantly said all those experts are wrong and he's right".
But former Prime Minister John Key was no fan of Treasury either, calling their predictions "a load of nonsense" in 2016.
"They can't get predictions in 44 days right, let alone in 44 years… They constantly get it wrong."
Mr Barclay said Mr Twyford will have learned his lesson.
"I suspect it's a one-off incident, and I'm sure the minister will reflect and not do it again."