Environmentalists have complained about gas producer Santos to the corporate watchdog and the Australian stock exchange.
Environment Centre Northern Territory says the company, Australia's second-largest independent gas producer, may have made false and misleading statements to the market about a massive gas project.
"Santos has been speaking out of both sides of its mouth when it comes to its Barossa gas project," director Kirsty Howey said on Thursday.
Ms Howey alleged that Santos told the Federal Court in June, during its losing court battle with traditional owners, that delaying offshore gas drilling would cost hundreds of thousands of dollars per day.
"But then in November, when the Federal Court rejected its bid to restore a drilling licence, the company told the market that, despite a delay of months, there would be no materials cost impact and the project timetable would stay on track," she said.
"Santos can't have it both ways. Misleading markets is a very serious matter."
ECNT said it had referred the statements to the Australian Securities and Investments Commission and the ASX in a bid to ensure Santos adhered to public expectations and the law.
"Santos must be compelled to provide the market with full and frank disclosure of the expected impact of the Federal Court's most recent decision on the Barossa project, so investors and the public are fully informed," Ms Howey said.
The environmental group's lawyers, The Environment Defenders Office, said Santos gave sworn evidence in the court about the cost and potential impact on scheduled work and detriment to third parties resulting from a potential six-week delay.
"Santos has now been delayed almost three months and who knows how long that delay will continue," lawyer Alina Leikin said.
The Santos-led Barossa offshore natural gas development plans to pipe gas about 280km past the Tiwi Islands, to the Darwin LNG facility, with the first production expected in 2025.
The company lost a bid earlier this month to restart drilling on the $US3.6 billion project when the Federal Court dismissed its appeal against an earlier ruling that the offshore gas regulator should not have approved drilling in the gas field.
The drilling, which started in July, was happening in waters down to 376 metres deep, about 33km from the Oceanic Shoals Australian Marine Park.
It stopped after Tiwi Islander and Munupi man Dennis Tipakalippa launched the legal action against Santos, claiming he was not consulted over the company's environmental plan.
Federal Court judge Mordecai Bromberg ruled in Mr Tipakalippa's favour in September, finding the regulator should not have approved the environmental plan.
He ordered the approval to be set aside.
In a statement after the company lost its appeal, Santos said it would revise its environment plan for the Barossa project and apply for all remaining approvals following the court ruling.
"Santos does not anticipate any material cost or schedule impact and first gas from the Barossa gas project remains on track to be delivered in the first half of 2025," it said.
The company has previously also said the project, which was 43 per cent complete and on schedule before the September court decision, is one of the world's lowest-cost new LNG supply projects and it will give Santos and Darwin LNG a competitive advantage in the tightening global market.
The National Offshore Petroleum Safety and Environmental Management Authority accepted the project's environmental plan and approved the drilling activities in March, saying it was satisfied the project had complied with the regulations.
Santos has been contacted for comment.
The Tiwi Islands are 85km north of Darwin.
