Shipping operations at the world's largest coal port could be disrupted by a planned "protestival" even if a planned two-day blockade does not go ahead.
An event scheduled for later in November is due to involve live music and workshops as well as a 50-hour blockade of the Port of Newcastle.
But NSW Police have asked a court to deem it an unlawful assembly, rendering anyone who stops port traffic liable to be arrested.
Organisers Rising Tide said the event from November 22 to 24 would be one of the world's most significant climate protests, with demonstrators in canoes and kayaks blocking the port.
Ahead of a hearing on Friday, protesters gathered outside the NSW Supreme Court, criticising the need to be there.
"We're calling on NSW Police to stop wasting public resources by fighting peaceful protesters and protest movements and taking them to court," NSW Council of Civil Liberties vice-president Lydia Shelly said.
Lachlan Gyles SC, acting for the NSW police commissioner, told the court the dispute was over methods rather than messages.
"The police are not trying to stop people expressing views about this issue, it's an important part of democracy to be able to do that, the question is how it's done," he said.
Justice Desmond Fagan said there appeared to be clear safety risks from the planned protest in the water, where small vessels could end up in the passage of difficult-to-manoeuvre bulk carriers.
But planned actions on land appeared less dangerous.
"Listening to the music probably won't hurt them either," Justice Fagan said.
Rising Tide's barrister Neal Funnell said it was unlikely small and large vessels would be in the water together.
"There is no realistic prospect of the port remaining open if the application by the commissioner is refused," he said.
Justice Fagan said protesters were effectively asking the court to authorise shutting the port for two days, a move he described as a "very ambitious resistance" to the police bid.
Mr Gyles said prohibiting the blockade but allowing nearby land-based events to go ahead would still encourage civil disobedience.
"People would be very likely to enter the water and attempt to block the harbour anyway," he said.
Port of Newcastle harbourmaster Vikas Bangia said the possibility of a shutdown would be enough to leave ships stranded in the harbour or drifting offshore, creating backlogs in supply chains.
"If there is any doubt, then the suspension of shipping will take place," he said.
NSW Police Assistant Commissioner David Waddell said protest action on land would make it hard to launch vessels into the water, potentially delaying responses to emergency incidents such as rescues.
He managed police operations as similar kayak-based protests took place in 2023, when 109 people were arrested after remaining in the water beyond the advised 30-hour period.
The most severe penalty was a $400 fine and the majority of those arrested were not prosecuted, Mr Waddell noted, but those paddling in the water appeared "extremely inexperienced".
The court was told attendance would be around 5500 people across the event, but a smaller number were expected to participate in the blockade.
The case will return to court on Tuesday.
