Last minute changes to the controversial Health and Safety Reform Bill could risk the right to a fair trial, warns the Law Society.
The additions were made to the legislation after the select committee had finished hearing submissions, so there was no public scrutiny on the changes.
The additions included allowing the directors of the government's spy agencies the right to declare that parts of the legislation did not apply to their staff in cases of national security.
The committee also added a new schedule to the bill introducing a "closed material procedure" for court proceedings.
Austin Forbes QC - the convenor of the Law Society's Rule of Law Committee - said that meant that evidence could be withheld if the material was deemed to be classified security information.
"You are weighing here the confidentiality of security-sensitive information in the national interest as against the rights of a person, particularly in a criminal trial, to a fair trial."
He said there was also the question of what was considered classified security information.
"Who's to say whether the information should be made available to the accused, if the judge says yes, after the judge presumably has had a security clearance, is there a capacity for it to be overruled by the Prime Minister or Attorney-General?"
Attorney-General Chris Finlayson said the Law Society had got it wrong.
He said the part of the bill that the society was referring to was amended in the committee stages of the parliamentary debate.
He said he was disappointed at the lack of rigour shown by the Law Society.
"The Law Society plays an important role in contributing to the quality of legislation passed by Parliament.
"But in order for Parliament to benefit from that contribution, accuracy really is paramount, especially when the Law Society chooses to comment on legislation via press release."
The legislation passed its committee stages last night, so now just has a third and final reading before it is passed.