Lawyers representing Tiwi Islanders trying to stop a gas pipeline running through their traditional sea country have been ordered to pay more than $9 million to gas giant Santos for its legal costs.

It's unusual for lawyers to be required to pay costs when their clients lose a case. But in this instance, the judge ruled the Environmental Defenders Office (EDO) had engaged in "a form of subtle coaching", and effectively became a party to the case.

Santos pursued the EDO for all of its costs and was successful, with the parties agreeing to a sum of $9,042,093.05.

Santos is building a 262-kilometre pipeline from its new Barossa gas field in the Timor Sea to a processing plant in Darwin.

The Tiwi Islanders, led by Simon Munkara, had argued the pipeline would impact on culturally significant sites that represented the Ampiji rainbow serpent and Crocodile Man.

Justice Charlesworth ruled in the Federal Court that the expert reports relied on by the Tiwi Islanders had been manipulated, and could not be relied on.

In January, Justice Charlesworth ruled in Santos's favour, and ongoing hearings about costs have followed.

Santos said in a statement that the EDO was found to be an active participant in a broader "Stop Barossa Gas" campaign, which aimed to disrupt, delay and shut down the Barossa Gas Project.

EDO chief executive David Morris said in a statement the organisation decided resolving the claim now was in the best interests of its clients, staff and organisation.

"Throughout this matter, EDO has diligently adhered to client instructions. We have also treated the court's findings with the utmost seriousness," he said.

Environmentalists and public interest law advocates have argued Santos' pursuit of the EDO is a form of "SLAPP suit" — a strategic lawsuit against public participation.

EDO vows to continue fighting for climate 

The payout appears serious for the EDO, given its current financial position.

In its most recent annual report up to July 2023, the EDO had revenue of about $13 million, and ran a loss of nearly $900,000. It had less than $9 million in cash and equivalent assets.

Mr Morris said the EDO had a "formidable track record of success for its clients" over its nearly 40-year existence.

"We look forward to continuing to provide public interest legal support to communities fighting to keep the climate safe, defend cultural heritage and protect the species and places they love," he said.

"Our role has never been more critical."

In its statement, Santos said: "The Barossa Gas Project and the associated Darwin LNG Life Extension project will create around 600 jobs throughout the construction phase and secure around 350 jobs for the next 20 years of production at the Darwin LNG facility.

"It has been publicly reported that the NT Government estimates $2.5 billion worth of wages and contracts will flow to Territorians from the projects during that time."

Legal battles and documents

In the wash-up of Mr Munkara and the EDO's loss, Santos successfully subpoenaed the EDO for a large tranche of documents, detailing communications between the EDO and other members of the Stop Barossa Gas campaign including the Environment Centre NT and the Sunrise Project.

Those documents have not been made public, and it's not yet clear whether anything in those documents will result in further litigation.

Meanwhile, Santos is defending another legal action by clients represented by the EDO, who are arguing the company misled investors when it said it had a plan to achieve net zero emissions by 2040.