The Refugee Action Coalition (RAC) said they would ignore a Supreme Court decision that declared Saturday's event a prohibited public gathering.

In a judgement handed down late on Thursday, Justice Michael Walton granted a NSW Police application that opposed the rally on public health grounds.

The rally, which is being organised by the Refugee Action Coalition (RAC), is scheduled to take place at Sydney's Town Hall on Saturday afternoon.

Immediately following the decision, during which Justice Walton said the right to protest did not outweigh health concerns, the group's spokesman said the ruling would not change their plans.

"We'll still be holding an event this Saturday, urging people to participate," James Supple said outside court.

"As the court said, it doesn't actually make it illegal to come to a protest, it just gives the police more powers.

"We'll be doing everything in our power to ensure it's a safe gathering and urging people to show some safety concern for the coronavirus measures."

Police had asked RAC to postpone the protest, which is expected to attract around 150 to 200 people.

But the group's lawyer, Emmanuel Kerkyasharian SC, told the court the protest was a matter of urgency given refugees were being held in custody against their will.

He also argued the rally was no different to gatherings that were allowed in schools, airports and parliament.

Mr Supple said RAC did not intend to take their case to the Court of Appeal and would instead push ahead with the protest in spite of warnings from authorities.

NSW Police have already warned that any protester breaking the public health order will be fined $1000 and asked to move on, and if they do not comply will be arrested.

"I want to be clear about this - if people choose to break the law and attend this protest, police will not hesitate to take the appropriate action against them," Assistant Commissioner Mick Willing said in a statement.

NSW Police lawyers on Thursday night told the court protesters were playing "Russian roulette" and could not guarantee against the spread of the coronavirus at the event.

Police Minister David Elliott pointed out that a protester, who attended last weekend's Black Lives Matter rally in Melbourne, tested positive for the coronavirus on Thursday.

"I urge those thinking of protesting despite the Supreme Court decision and against the health advice to promptly reconsider their plans," Mr Elliott said.

"NSW Police will be out in full force over the weekend to issue fines against those flouting the health orders.

"If you disregard the move-on directions of police officers, you can expect to be arrested."

Australian Associated Press