The sausages and onions sizzle on the barbecue on Colin Butland's front lawn in suburban Bullsbrook in a setting that looks like any other community gathering.

Key points: A recent High Court decision has changed the way class actions are funded

A recent High Court decision has changed the way class actions are funded It has impacted a planned class action billed as Australia's biggest ever

It has impacted a planned class action billed as Australia's biggest ever 40,000 people could be eligible to join the action over toxic PFAS chemicals

But at this address in Perth's north, representatives of Shine Lawyers are sitting on plastic chairs and talking to locals.

They are explaining their planned class action against the Federal Government, with the hope of signing up the 500 Bullsbrook landowners who are eligible to sue over their property value losses due to contamination by toxic firefighting chemicals (known as PFAS) used at nearby RAAF Pearce air base.

Bullsbrook residents Gary and Karen Breadsell, and Colin Butland have all signed up to the class action. ( ABC News: Hugh Sando )

Bullsbrook is the first stop for Shine as it works its way around the country.

It is a markedly low-key and grassroots approach by the law firm — and one which the approximately 40,000 people around Australia who are eligible to join the class action can expect to experience.

Bullsbrook resident Colin Butland turns the sausages for a class action community barbecue. ( ABC News: Hugh Sando )

It is also a very necessary strategy to keep this class action alive, with a High Court decision in December creating uncertainty about how class actions are funded.

Legal experts say it is likely many other law firms looking to file class actions will also be approaching potential clients this way — and it is important that if this is you, you understand your rights.

Uncertainty over Australia's biggest class action

The High Court decision cast uncertainty over the use of common fund orders, which are a mechanism for lawyers and litigation funders to be paid their fees for a class action.

It may sound like an irrelevant legal technicality but these orders have a big impact on whether a litigation funder, which bears the upfront costs, decides to invest in a particular class action or not.

These orders give lawyers and litigation funders the confidence at the beginning of the legal process that they can take their fees from the total settlement from a class action, regardless of whether claimants have signed a funding agreement with them.

As a result, there was previously little pressure to sign up big numbers of people to class actions to ensure they proceeded.

Legacy issues from toxic chemicals in firefighting foam remain a national issue. ( CRC CARE )

But now, there is some uncertainty around this particular PFAS class action, which has been billed as Australia's biggest ever, involving eight sites across Australia.

Shine's plan to file the class action by last Christmas was derailed by the High Court's decision and Shine now needs to reassure its litigation funder LCM — which bears the upfront costs of the legal action — the action is financially viable.

It is a setback for the firm, which made a high-profile announcement, using the star power of environmental campaigner Erin Brockovich, that this class action was going ahead just three months ago.

Shine is trying to get as many people as possible to sign two agreements, one appointing Shine Lawyers as its legal representative and the other committing them to paying a percentage of any successful settlement to the litigation funder.

Shine's head of class actions Jan Saddler said the High Court decision had led to the company returning to the practice of building some class actions through a mixture of grassroots campaigning and community gatherings, like in Bullsbrook.

"The High Court decision does not impact the merit of this PFAS class action and we will continue to fight for compensation on behalf of residents whose property prices have plummeted as a result of environmental contamination," she said.

Shine can count Mr Butland and his fellow Bullsbrook residents Gary and Karen Breadsell as successes after they signed up on Friday.

Bullsbrook resident Colin Butland and his son Duke, 3, live next to RAAF Pearce. At one point they were drinking bottled water over concerns about contamination. ( ABC News: Rebecca Turner )

They all say their land has been tainted by the "stigma" of contamination, caused by the Department of Defence's use of toxic chemicals and through no fault of their own.

Bullsbrook residents Gary and Karen Breadsell have had problems selling their property. ( ABC News: Hugh Sando )

"I never thought we would be put in this position to have to sue our own Government to get them to wake up," Mr Butland said.

One of the class action's lead applicants, Reannan Haswell, said she was sick of the Federal Government's lack of action in funding long-term solutions to Bullsbrook's safe water supply problems and providing compensation for a drop in land values.

PFAS class action client Reannan Haswell (second from left) with her partner, their three children and American activist Erin Brockovich (right). ( Supplied )

"We have lost our financial ability to leave [our property]," she said.

"Legally and morally, we can't sell it."

What should you know before signing up to a class action?

Class actions are broadly considered to be a cost-effective and efficient way of people being able to access justice.

Consumer Action Law Centre chief executive Gerard Brody said class actions were also a lower-risk option, compared to individuals taking their own legal action.

But he said there were three important things anyone thinking of signing up to a class action should be aware of.

First, they should assess if the fee to be paid to the litigation funder was fair.

Mr Brody said a fee of between 20 and 25 per cent of the client's settlement was common.

"40 per cent is not particularly fair," he said.

Second, you do not have to sign up to an open class action, unlike with a closed class action, and you can opt out during the court process.

Open class actions, like the one involving Bullsbrook, involve a lead plaintiff bringing the action on behalf of all people who could potentially be affected but have not necessarily signed an agreement.

Third, you should ask how conflicts of interest were managed, Mr Body said.

This could include ensuring that decision making around making a settlement was taken after getting an external legal opinion.

"There's always a conflict of interest between lawyers and their clients," he said.

"For example, a lawyer might decide to settle [the class action] so that they can get paid."

Law professor Michael Legg, from the University of New South Wales, recommended anyone concerned about conflicts of interest to get independent legal advice.

He said it was important to remember you were signing an agreement with lawyers who had a financial interest in the class action proceeding.

Law professor Michael Legg recommended clients get independent advice if they were worried about conflicts of interest. ( Supplied: Michael Legg )

"They are being asked to sign these things by people who will benefit from them signing," he said.

Professor Legg argued the High Court's ruling had made class actions more difficult for plaintiffs.

He said common fund orders had allowed the court to review the fees that plaintiffs would pay, with a trend of courts reducing the fees in their favour.

The new pressure on law firms to sign people up to class actions to ensure funding meant that plaintiffs often had to make a decision to commit at an earlier stage and perhaps before they were convinced it would be successful.

"You think you have a good claim but you don't know," he said.