Making people on bail wear alcohol or drug-detecting bracelets is a "major infringement of liberty", the Law Society says.
Parliament is considering a law change that will allow police and corrections to require bailed people or community-based offenders to undergo drug-testing if they have abstinence conditions imposed on them.
The Law Society told a select committee today it had concerns about the proposed regime's absence of judicial oversight and its potential inconsistencies with the Bill of Rights.
Spokesman Graeme Edgeler said a proposal for continuous monitoring with a drug monitoring device was a "major infringement of liberty".
"It will be possible to justify it in some circumstances, but certainly not in respect of all people who are subject to alcohol or drug abstention conditions," he said.
The finer detail about the drug-testing regime will be established by the Department of Corrections chief executive and the Commissioner of Police once the bill passes.
The Law Society said in its written submission that because the rules had not yet been made, it was impossible to judge their consistency with the Bill of Rights. But it said the potential for mandatory blood tests was likely to raise concerns about unreasonable searches.
Mr Edgeler told the committee that even prisoners did not face mandatory blood tests.
"It seems wrong that we would allow police and corrections to write rules that allow themselves to blood-test people who aren't even in prison."
In introducing the bill, Corrections Minister Sam Lotu-Iiga said principles were written into the bill to guide officials in setting up the drug-testing regime.
These included a requirement that the testing could not be unreasonably intrusive or frequent and that the person should be given as much privacy and dignity as possible.
Mr Edgeler also said the requirement for some people to be monitored around the clock lacked oversight by the courts.
"No person should be required to wear an alcohol monitoring bracelet without a judge's approval," he says.
At the bill stands, discretion about drug and alcohol testing will be in the hand of police and corrections officials, who are also responsible for writing the rules.
Police Association vice-president Luke Shadbolt said his organisation supported the legislation because drug and alcohol abuse were major drivers of crime.
But he said that unless bailees or community-based offenders were also able to get access to addiction treatment then Government was "setting them up to fail".
The association recommended that a person who was required to be tested for drug use should also be ordered to attend drug counselling or other treatment services.