Coal is the biggest driver of climate change, and in fighting the climate crisis, civil society has a democratic right to freedom of expression, especially against the giants of the coal industry. This is exercised by drawing attention to the immediate and long-term dangers of coal, working with governments to ensure they make the right decisions, and campaigning to show the public just how bad fossil fuels really are.

The G7's commitment and the Lowy Institute data show that the transition to a low-carbon economy is gaining momentum, but what happens when fossil fuel companies try to stifle our right to freedom of expression?

In just a few days we will see, as Greenpeace Australia Pacific and Australia's biggest climate polluter, AGL Energy, face off in the Federal Court, in a case that could have huge implications for freedom of expression.

AGL initiated legal proceedings against Greenpeace Australia Pacific following the launch of a campaign calling AGL out as Australia's biggest climate polluter. This campaign is backed up by data from the Australian Clean Energy Regulator showing that the coal behemoth is responsible for 8 per cent of Australia's total emissions - that's more than twice the amount of the next biggest emitter of greenhouse gases.

AGL is not refuting that it is Australia's biggest climate polluter; it is arguing that logos identifying it should be removed from the campaign as they allegedly breach trademark and copyright.

This is an example of how powerful fossil fuel companies like AGL use unscrupulous legal threats and actions against charities, activists and community groups in order to limit freedom of expression. These suits, known as strategic lawsuits against public participation (or SLAPP suits), are brought against groups or people to silence, intimidate and censor them by burdening them with the costs of litigation.

In 2004, Tasmanian logging giant Gunns came under fire after it filed a $6.3 million SLAPP suit against environmentalists who opposed its logging operations. Bravus (formerly Adani) is suing activist Ben Pennings for multimillion-dollar damages, claiming he misused confidential information but admitting that it doesn't know what, if any, information was misused. A traditional owner was forced into bankruptcy by Bravus after numerous failed legal actions against the company's Queensland coal mine, and the NSW Minerals Council forced Newcastle-based group Rising Tide to take down its campaign website - an anti-coal parody of the mining industry's "Life: Brought to you by mining" campaign - for allegedly breaching copyright.

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SLAPP suits are weaponised abroad, too. In 2002, ExxonMobil (trading as Esso) launched unsuccessful legal action against Greenpeace France after it published caricatures of the Esso trademark on its website. The French Supreme Court held that the caricatures, which were used to criticise the environmental policy pursued by Esso, were protected on the grounds of freedom of speech.

In an open letter to AGL, a number of prominent charities, including the Australian Conservation Foundation and 350.org Australia, have described AGL's SLAPP suit as "an attack on civil society" and "a direct affront to free speech and the ability of organisations to hold corporations to account on climate change".

As members of civil society, we must fight back against SLAPP suits such as AGL's current case against Greenpeace Australia Pacific, because doing so protects our democratic right to freedom of expression. Democracy cannot exist without freedom of expression. It is a bedrock right that enables the participation of citizens in economic and social policy. This right is enshrined in international treaties our government has signed. It has been recognised by the highest court in our country. It is woven into our laws. It ensures people are able to discuss, exchange, and debate ideas without censorship or reprisal.

The outcome of this case could set a powerful precedent for freedom of expression, especially for those of us who stand up and hold the fossil fuel industry to account for being the main driver of climate change. Defeating this coal-fired SLAPP suit will allow other charities, not for profits, comedians and members of the community to exercise their right to freedom of expression in order to criticise, parody and satirise without fearing litigation.