Tasmanian anti-protest laws directly target implied freedom of political communication and are unconstitutional, lawyers for the former Greens leader Bob Brown will argue in the high court of Australia on Tuesday.

Brown, 72, was arrested under the controversial Workplaces (Protection from Protesters) Act 2014 in January 2016 at Lapoinya state forest near Burnie in Tasmania’s north-west.

He was the third person arrested under the laws, which carry a $10,000 fine for protesters found to have disrupted business activities. The second person to be arrested was registered nurse Jessica Hoyt, 36, who joined Brown in taking the challenge to the high court.

The Tasmanian government dropped the charges against Brown and Hoyt once they mounted the high court challenge but Brown said they continued the challenge to protect future environmental actions.

He said the laws were part of a broader movement in Australia to stamp out environmental objections to corporate projects and threatened to undermine Australian democracy.

“They simply don’t want the public to see what’s going on in these forests,” he told Guardian Australia. “They can’t win the environmental argument on its merits so they take out the environmentalists. They want you to be sidelined and unable to show what’s going on.”

Since the Hodgman government introduced the laws as an election promise in Tasmania in 2014, as part of that state’s long-running forestry wars, two other states tried to follow suit.

New South Wales succeeded, introducing laws that imposed a tenfold increase in fines for people protesting against coal seam gas and mining developments.

The former Western Australian government proposed similar laws but they were not enacted before the March election and have been thrown out by the McGowan government.

The WA government has also since withdrawn interest in Brown’s high court challenge, making it the only Australian government not represented at the bar table.

Emily Howie, the director of legal advocacy at the Human Rights Law Centre, said the support for the Tasmanian government shown by both the federal government and all states except WA was unusual and alarming.

“They will all be at the bar table arguing that these laws are valid,” she said.

The Human Rights Law Centre sought leave from the court to appear in the case and will be supporting Brown’s arguments.

“This is turning out to be an increasingly important case in terms of Australians’ ability to speak freely on political matters,” Howie said. “It’s raising a whole lot of really crucial constitutional issues.”

The Tasmanian government will argue that the laws do not breach the constitutional implied freedom of political communication because they are targeted at activities that interfere with legitimate business activity.

Lawyers supporting Brown will argue that the laws are nevertheless designed to suppress political protest and are not restricted to protecting private property owned by businesses.

“A loudspeaker or a megaphone on the street could disrupt business and could come under the auspices of the act,” Howie said. “The problem with the act is it is only directed at protesters … the law itself is a directed toward political communication. If you look at the circumstances in which Bob was arrested, you will see that he was on a public road.”

The hearing has been set down for one day.