A Privy Council ruling criticising the Court of Appeal has prompted lawyers to examine related law changes made last year to see if they were lawful.
In a decision from London released on Tuesday, the Council allowed a test case in which 12 convicted criminals wanted new appeals.
The law lords effectively struck down the way the court was dealing with criminal appeals where legal aid was refused.
New Zealand lawyers had argued Appeal Court procedures discriminated against the poor, denied them aid, and resulted in a "sham" of an appeal, or an apparently biased hearing of their appeals.
The court has been told to rehear the appeals, at which the appellants were guaranteed to be granted legal aid.
The decision has reignited debate over government moves to abolish ties to the Privy Council.
The Government moved last year to amend the Crimes Act, allowing Appeal Court judges to rule on appeals without open hearing in some circumstances.
Lawyers were now considering the legal grounds for the amendment, Auckland lawyer Marie Dyhrberg told National Radio today.
They would study the law change to see if it was consistent with the Privy Council ruling, which was based on human rights legislation.
"It may well be debatable whether the legislation, seeking to validate earlier legislation, is in fact itself lawful," Ms Dyhrberg said.
Law Society criminal law sub-committee chairperson Judith Ablett-Kerr said the change "really had to take place".
"Otherwise the whole thing would have continued to be an illegal process that was going on in the Court of Appeal," she said on National Radio.
Attorney General Margaret Wilson, a prime mover in examining links with the Privy Council, would not comment on the decision.
It was a "complex" case, and she was awaiting a report from the solicitor-general, her spokeswoman told NZPA.
Wellington lawyers Antony Shaw and Tony Ellis, who took the case to the Privy Council, yesterday described the decision as "momentous".
Mr Ellis said that beside the 12 cases taken to the Privy Council, many of the 1500 people who had received similar treatment were likely to get rehearings if they applied.
The 12 include convicted murderers Ian Douglas Johnson and Aerengaroa Timoti, convicted rapists James Bennett and Iosua Chankee, and Emelysifa Jessop and Osa Poni Savelio, who were convicted of aggravated robbery.
Opposition MPs pounced on the decision, with Act MP Stephen Franks calling it a "stinging rebuke" to government moves to abolish access to the law lords.
Mr Franks and National Party MP Wayne Mapp, both lawyers, hailed the decision as a reason New Zealand should preserve links with the Privy Council.
Dr Mapp, previously an associate professor of law, said the decision was a "clear warning shot" to the Government.
"This is the Privy Council saying that the criminal appeals system operated by the Court of Appeal was 'unlawful'," he said.
"An intellectually powerful Privy Council, detached from New Zealand, has been able to see the flaws in the Court of Appeal procedure," he said.
A second appellate court in New Zealand, as proposed by Ms Wilson, would not have that capacity, he said.