A LANDMARK High Court hearing which could enshrine freedom of speech in the Australian Constitution will be heard on Tuesday.

Thanks to Adelaide's controversial street preachers, the challenge could see free speech recognised as a Constitutional right - comparable to the US First Amendment - and trigger a rewriting of state and council laws that were drafted to stop people being able to "preach", "canvass" or "harangue".

Tuesday's hearing in Canberra has such widespread ramifications that South Australia's Attorney-General has been joined in the matter by the Attorneys-General for the Commonwealth, NSW, Victoria, Queensland and WA.

The Human Rights Law Centre has sided with the Adelaide street preachers Caleb and Samuel Corneloup.

High Court Chief Justice Robert French has made it clear the hearing will be about legal principles rather than religion, telling the preachers: "It will not really be anything to do with, as you would appreciate, the merits of your preaching".

At present there is no guarantee of freedom of speech written into the Constitution.

If the court decides in favour of the preachers it may opt for a narrow interpretation limiting such freedom to political speech - but the justices could use the case as a vehicle for a much broader and more significant decision regarding rights relating to freedom of communication.

The case was triggered by anger at the aggressive style of preaching in public spaces such as Rundle Mall.

Attempts to silence the preachers under Adelaide City Council bylaws, saw the preachers appeal to the full bench of the Supreme Court which in August 2011 ruled certain bylaws were invalid to the extent they prevented free political communication.

The State Government appealed to the High Court, with a spokesman for Attorney-General John Rau saying the appeal concerns the ability of the City Council to regulate its streets.

"It constrains the legislative and executive power necessary to maintain the system of responsible and representative government required by the Constitution," he said.

While the hearing is likely to take an hour, a decision could take months.

SA Law Society president Ralph Bonig said the decision had considerable implications.

"The legal community will be interested in the outcome given its potential for the concept of freedom of speech to be implied in the Constitution," he said.

Lawyer Peter Campbell of Kelly and Co. said the case had the potential to drastically alter the legal landscape.

"A number of legal restrictions and permit regimes may be invalid and unenforceable," he said.