Debates around judges and magistrates' ability to conduct discretionary sentencing in Western Australia will be thrown to the media today ahead of the proposed mandatory sentencing laws due to pass in Parliament this week.

DEBATES around judges and magistrates' ability to conduct discretionary sentencing in Western Australia will be thrown to the media today ahead of the proposed mandatory sentencing laws due to pass in Parliament this week.

In an unprecedented move, three peak WA legal bodies - the Law Society of Western Australia, the Australian Lawyers Alliance and the WA Criminal Lawyers Association - have joined together in a desperate and last minute bid to persuade the government and opposition parties in the Upper House to reconsider the legislation.

The legal bodies will today hold a media conference at the Law Society's office at Perth's St Georges Terrace in an effort to build some dialogue around the issue before the vote this week.

Tom Percy QC, president of the Australian Lawyers Alliance, said the proposal to introduce mandatory sentencing  in WA runs contrary to every established principle of fairness and justice.

"This is probably the biggest single injustice ever foisted upon the community in the State's history," Percy said.

"Mandatory sentencing has never worked, not in this state or anywhere else. The present amendments are reactionary and repressive. They are highly unlikely to deter offenders," he said.

Law Society of Western Australia president, Dudley Stow, said the Society opposes mandatory sentencing because the circumstances of offences and offenders are so varied that courts need discretion to properly sentence people convicted of assaulting public officers.

“Mandatory sentencing removes judicial discretion and will result in injustice,” said Stow.

“We acknowledge the need to protect our police officers and emergency workers and ensure their safety whilst serving the community; however in this instance the courts should retain their existing discretion in determining sentences on criminal charges.”

Stow said the proposed laws are unlikely to achieve their desired purpose of decreasing assaults on public officers; and would only lead to cases where blatant injustices would arise.

Stow said there will always be the odd case in which imprisonment is not appropriate, and that the removal of the court's discretion will result in unjust outcomes.

"These amendments are, by any standard, bad law," he said.

The three bodies are now calling on the National and Greens members in the Legislative Council to consider amendments that have been before the Lower House, which they say could give the court the power to refrain from mandatory sentencing where the outcome would be unjust.