Opposition MPs have accused the Government of undemocratic law-making after a controversial bill was passed without public input and with official advice heavily censored.
Legislation which allowed people who cared for disabled family members to get paid by Government was passed into law on Friday under urgency.
The New Zealand Public Health and Disability Amendment Bill would also prevent any carers from taking legal action against Government on the grounds that they were being discriminated against.
Opposition members slammed the Government's rush to change the law and the lack of transparency around the process.
It was passed into law a day after it was introduced by Health Minister Tony Ryall and without going before a select committee.
A Regulatory Impact Statement (RiS) for the bill prepared by the Ministry of Health was heavily redacted, with entire pages blacked out.
Labour Party disability issues spokeswoman Ruth Dyson said she had never seen such a heavily redacted statement: "It is unprecedented."
She said the refusal to publish some official advice was highly inappropriate given the controversial nature of the legislation.
A report by Attorney-General Chris Finlayson found that the clause which prevented carers from making a legal challenge breached the Bill of Rights Act because it limited the right to seek a judicial review.
Legal expert Andrew Geddis said that the implications of the law change were highly significant.
In a blog on the website Pundit, he wrote: "The judiciary's primary function - to declare the meaning of law and its application in particular cases - has been nullified.
"Furthermore, the judiciary's role as protector of individual citizens in terms of ensuring that they are being treated in accordance with the laws of the land has been removed.
"While the stakes may be small in the immediate case, this is about as big a deal as it gets in terms of our constitution."
In introducing the bill in Thursday's Budget, Mr Ryall confirmed that $23 million would be allocated to pay people who cared for a disabled adult family member.
It was a response to a legal case which found that the Government was discriminating by not paying family carers.
The bill was supported by National, Act, United Future and the Maori Party, and opposed by Labour, Greens, New Zealand First, Mana and Brendan Horan.
The new policy did not extend payments to spouses of disabled adults or parents of disabled children.
Mr Finlayson's report on the bill said that not extending payments to all family carers could also be a breach of the Bill of Rights Act.
Officials reported that if all carers for adults with high or very high needs were paid - including spouses and parents of disabled children - the cost to Government would increase to $40 million.
Payments were also limited to adults who were assessed as having high or very high needs.
There were estimated to be around 5600 disabled adults being cared for by family members, 1600 of these who were assessed as having high needs.
If payments were extended to all carers and all disabled adults - not just high needs - the cost to Government would jump to $65 million.