New legislation touted as the biggest shake-up of the legal system in 50 years could see innocent people jailed, worried lawyers say.

The Criminal Procedure Bill, now before the Justice and Electoral Select Committee, has passed its first reading, with a second reading set down for July.

But members of the Waikato legal fraternity are concerned.

Waikato-Bay of Plenty Law Society president Bruce Hesketh says two of the bill's proposals could threaten the right to a fair trial.

He said raising the threshold for jury trials and having to notify the prosecution of any issues in dispute before going to trial was an attack on the rule of law.

"This isn't about lawyers complaining about missing out on money this is about people's rights," he told the Times.

Justice Minister Simon Power, who introduced the Bill, refused to comment on Mr Hesketh's concerns about the proposed legal system changes, when approached by the Times.

Through a spokeswoman, he said he could no longer comment because the Bill was now before the select committee.

However, last year when the Bill was first touted he said it had the potential to save $24 million over five years and free up 16,000 court sitting hours a year.

Mr Hesketh said one of their biggest concerns was the proposed change in the threshold for jury trials.

The change would mean only people accused of crimes with a maximum penalty of three years in prison or more would be eligible for trial by jury.

All others would have to go before a judge alone.

Mr Hesketh said the proposed change was "abhorrent to a democratic society".

He said the right to trial by jury had been part of Common Law for 800 years and was there to protect innocent people from being sent to jail by "overzealous" prosecutors or biased judges.

"Sending an innocent person to prison has got to the the worst thing any society could do to its own citizens," he said.

He was also concerned that the increased workload on judges could lead to mistakes being made.

Mr Hesketh said his colleagues were also concerned at having to notify the prosecution of any issues in dispute before going to trial.

That proposed change would see a shift in the burden of proof and an accused's right to silence, he said.

It would also allow the prosecution to "patch up" any holes in their case before going to trial.