The Baird government is at loggerheads with the legal fraternity as the peak body for NSW barristers warns of the creeping expansion of police powers in the state when rates of crime are falling.

The Bar Association has been on a collision course with the state government over a raft of law and order proposals, including "serious crime prevention orders" that could be made by a court on the application of the NSW Police Commissioner even when a person had not been charged or convicted of a crime.

The association has now taken aim at another controversial bill which would allow a senior police officer, rather than a court, to make a "public safety order" to ban a person deemed a serious risk to public safety from a public place or event.

Lawyers have raised concerns the government's law and order policy reflects an "erosion" of the traditional role of the Attorney-General, Gabrielle Upton, who is a junior minister in the Justice Department. The department is headed by Deputy Premier and Justice and Police Minister Troy Grant, a former police officer.

Barrister Alister Henskens, SC, the Liberal MP for Ku-ring-gai, used a column in the News Corp press to accuse members of the association of "running political agendas for years", a claim rejected by its president, Noel Hutley, SC.

The association said in a submission to government that "no case has been made" as to why the powers to make public safety orders "should be conferred on the police at all, let alone in circumstances where it is recognised that rates of crime in NSW are declining".

The proposed orders would "restrict the freedoms of persons in NSW, including children and persons with impaired intellectual functioning, irrespective of whether they have committed or are likely to commit a criminal offence".

The subject of a public safety order order could only appeal to the Supreme Court if the order exceeded 72 hours.

The association said there was "a real doubt about the constitutional validity" of some sections of the bill, which may infringe the implied freedom of political communication.

The bill attempts to avoid this pitfall by carving out cases in which a police officer believes a person is likely to be attending an event to engage in "non-violent advocacy, protest or dissent".

But the association said this was "a pale shadow of the protection afforded to political speech under our Constitution" and a court was likely to strike down the law as invalid.

A spokeswoman for Mr Grant said the government was "confident" the proposed laws would "withstand any constitutional challenge".

"We always welcome falling crime rates. However, we have no intention of being complacent when it comes to combating serious threats to public safety or security," the spokeswoman said.

The changes were announced as an election commitment in March 2015, before Mr Grant took on the police and justice portfolio.

Ms Upton said she was "fully supportive of these vital measures and will speak to the bill in Parliament this week."