The Supreme Court will on Friday hear an attempt by the NSW Police to deem the in-water obstruction of the Port of Newcastle an unauthorised assembly.
That would leave protesters liable to arrest for blocking port traffic.
A similar blockade in 2023 featured 3000 people in kayaks and other vessels stopping coal ships for 30 hours.
More than 100 people were arrested after refusing to exit the water after the police-approved end of the protest.
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Organisers Rising Tide said the 2024 event, from November 22 to 24, would be one of the most significant climate uprisings on the planet.
The Port of Newcastle is the world's largest coal export port, sending about 144 million tonnes of the fossil fuel worth $38 billion offshore each year.
Police opposed the 2024 blockade because it would lead to serious delays at the port, the government said.
"This is a massive overreach from a government which wants to quash criticism because they know that they have a terrible record on climate," lawyer and organiser Briohny Coglin said.
"Our community is rightfully concerned about the climate crisis and are coming together to peacefully call on our government to take stronger climate action.
"The Minns government should be listening to these concerns, not trying to suppress dissent."
Peter Garrett is among dozens of musical acts due to perform at the multi-day protest. (Jason O'BRIEN/AAP PHOTOS)
Midnight Oil frontman and former federal environment minister Peter Garrett and ARIA award winner John Butler are among 30 musical acts due to perform on the protest sidelines.
Premier Chris Minns on Tuesday said placing obstacles in the way of the port harmed the key source of revenue to transition the economy to net-zero emissions.
"The state's biggest export as of today is still coal," he said.
"I know people don't like saying that.
"They don't like hearing it, but that's the truth. And until we get other industries up and running and pumping in the Hunter, that is going to be a key source of revenue to transition that economy and I'm not switching it off tomorrow."
Premier Chris Minns says coal remains NSW's biggest export and is vital to the economy. (Darren Pateman/AAP PHOTOS)
The Greens said organised protests such as the planned blockade were essential in a functioning democracy and would likely still go ahead, regardless of authorisation.
"This one has the support of so many people," MP Sue Higginson said.
"Iconic Australian author Tim Winton just last week was encouraging people to get to the protest and the line up of acclaimed artists who will be performing is testament to support and the need for this gathering."
Police Minister Yasmin Catley and NSW Police have been contacted for comment.
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