A class action lawsuit on behalf of the world's children could delay federal approval for the Vickery extension project near Gunnedah.
Whitehaven Coal's Vickery Extension Project would double the size of an approved coal mine and won approval by the state Independent Planning Commission in August.
It is now before the Commonwealth Environment Minister but an injunction was filed against it in the Federal Court on Tuesday.
They intend to argue doing so would violate her common law duty of care to young people around the world.
"There's no denying that there is harm today from climate change," he said.
"This case looks at the contribution of the coal that will ultimately be burnt from the Vickery Extension Project to climate change in the future. And it looks to future harm that that in turn will cause the applicants and the group members resulting from its contribution to climate change."
Mr Barnden estimated it could take as long as six months for the claim to be properly heard in the Federal Court.
He is suing on behalf of a group of eight Australian children, a "class" that is claimed to represent every person in the world under the age of 18 born up to September 8, 2020.
"It's precisely lawfare. It is a case taken by people who are not going to lose their job, not going to be affected really, by the actions," he said.
"And they don't have to live the consequences of their actions in the current term. They will argue in the longer term they do."