The Adani mining company’s “legal intimidation” tactics against community groups are a “threat to democracy” and “gravely concerning”, say eminent members of the legal profession, including a former supreme court judge and an expert on corporate lawfare.

The ABC reported on Tuesday that a law firm hired by Adani, AJ & Co, wrote a strategy document urging the Indian miner to “play the man” and adopt an aggressive legal posture against opponents.

The documents suggested Adani should trawl social media for evidence of bias among activists and decision makers. It recommended using the legal system to bankrupt poorly resourced opponents, silence commentators and put pressure on government.

Adani released a statement that said it made no apology for pursuing the company’s legal rights, but declined to say whether it endorsed or enacted the AJ & Co proposal. Guardian Australia has confirmed Adani engaged AJ & Co for the purposes of conducting commercial litigation after the strategy was pitched.

Community groups, Indigenous traditional owners and journalists have all confirmed recent interactions with AJ & Co, acting on behalf of Adani, in a manner consistent with the strategy document.

Brian Walters, a Melbourne-based QC and human rights advocate, is an expert on so-called Slapp suits – strategic lawsuits against public participation. He wrote the 2005 book Slapping on the Writs and said using the law to silence community groups undermined the democratic process.

“It is a fundamental feature of free speech that people should be allowed to comment on the way that corporations and other powerful people are using their power,” Walters said.

“What appears to have happened here is a large corporation has agreed to use, or has tried to use, threats of legal intimidation to silence the public in speaking out about its proposals.

“When corporations attempt to use the law not to achieve a legitimate forensic outcome but to intimidate those who criticise them, they are abusing the process of the law. They are bringing the law and indeed their own corporation into disrepute.”

His comments were echoed by another QC, retired Queensland supreme court judge Alan Wilson, who is also the patron of the Environmental Defender’s Office in Queensland. Wilson rarely makes public comment.

“The strategy outlined in media reports is both extraordinary and gravely concerning,” Wilson said.

“It is profoundly disturbing that lawyers working within our system of justice would believe, or represent, that their job is to be ‘trained attack dogs’ and that their client should regard itself as ‘involved in a war’ that might require ‘all out attack’.

“It shows a fundamental misconception of the lawyer’s role, which is to advance the interests of justice.”

Walters said that Slapp cases were not as common in Australia as the US, but many were dealt with quietly and “people often fold”.

Adani has previously labelled legal action seeking to stop the Carmichael mine frivolous and attacked the tactics of anti-coal activists. The strategy document described the situation as a “war”. Walters said these were not justifications for a lawfare retaliation.

“If lawsuits are frivolous, let them be defended on that basis,” he said. “That doesn’t justify you in threatening to bring lawsuits for an improper collateral purpose, namely to silence people.

“For [community groups], any legal action is threatening of their financial viability. It’s just small change for a corporation like Adani.

“I think no lawyer should propose using the law in a way that intimidates members of the public from exercising their democratic right to speak out about abuse of power. If that has happened, that should be contrary to the whole purpose of having lawyers.”

AJ & Co did not return calls from Guardian Australia. The firm told the ABC it would not comment on matters related to clients.

Adani said it had accounts with a panel of law firms for various purposes.

“We will not comment in detail on the legal firms we use, their marketing material, and any matters where they may represent us or advice we may receive,” the company said in a statement.

The Environmental Defender’s Office Queensland said on Tuesday it had received a legal letter sent on behalf of Adani on 12 September “clearly designed to intimidate us”.

“Instead of spending its legal energy on complying with Queensland’s laws, Adani is hiring lawyers to silence its critics in a well-funded campaign of intimidation, EDO Queensland’s chief executive and solicitor Jo-Anne Bragg said.

A faction of Wangan and Jagalingou traditional owners, who have been fighting a long-running native title case against Adani in relation to the Carmichael mine, said they had been targeted by the “malicious” tactics.

AJ & Co represented Adani as it pursued bankruptcy proceedings against the W&J man Adrian Burragubba over unpaid court costs.

“Adani’s attempt to bankrupt me is clearly guided by this litigation strategy and is an abuse of the legal process,” Burragubba said. “We can reveal we have previously received threats of massive economic torts and damages from AJ & Co unless we stop speaking out. We will not be silenced.”

The ABC reporter Mark Willacy said on Twitter that AJ & Co, acting on behalf of Adani, had lodged freedom of information requests to access his expenses and documents related to a story on the company.