A notice filed to the High Court on Monday by Crown Solicitor Michael Sexton reveals NSW Attorney-General Gabrielle Upton is seeking to support the Tasmanian government.

In January, Mr Brown was among five people charged under Tasmanian anti-protest laws while protesting the logging of 49 hectares of the Lapoinya forest in the state's north-west.

Police later dropped the charges but Mr Brown and another protester, nurse Jessica Hoyt, are pursuing their legal challenge against the laws, designed to prevent the disruption of mining and forestry projects.

Protesters face on-the-spot fines of $2000 for hindering a business activity and penalties of up to $50,000 or five years in jail for threatening to damage a business.

On October 26, NSW proclaimed its own new laws cracking down on "interference with mining and other businesses or undertakings".

They provide a maximum penalty of $5500 for anyone convicted of interfering with a business and putting people's safety at serious risk.

A maximum penalty of seven years in jail applies for anyone convicted of "intentionally or recklessly interfering with a mine".

A spokesman for the department of justice said NSW intervened in the High Court because "it is the issue of the extent of implied freedom of political communication, which is important to a State or Territory's legislative powers".

He said it was "normal" for attorneys general to intervene to make submissions on the constitutional point raised and the decision was Mr Sexton's.

Victoria had also intervened and he expected other states and territories would follow suit.

Mr Brown said the NSW government "has intervened in a High Court challenge by forest defenders against the Tasmanian government's draconian anti-protest laws".

"Liberal governments in Tasmania, NSW and Western Australia, under pressure from logging and mining corporations, have all moved to impose restrictions on the rights to political communication" which he and Ms Hoyt say are implied in the Australian Constitution.