The passing of contentious bail laws in New South Wales that have outraged Indigenous, legal and Human Rights groups will only be the start of a major campaign, the Aboriginal Legal Service said on Friday.

The laws, which the government has admitted will likely see more children spend time behind bars, passed NSW Parliament on Thursday evening, with Attorney General Michael Daley arguing his government were "aware of concerns" but had approached the change cautiously.

Premier Chris Minns agreed, telling ABC Radio on Friday the laws struck the right balance, and disagreed with accusations the changes were a "betrayal" of young people, despite criticism from groups across the state, as well as members of his own party.

Under the new laws, a judge will need a high degree of confidence a person aged between 14 and 18 will not commit a further serious indictable offence whilst on bail, before granting bail.

On Friday, the Aboriginal Legal Service (ALS) NSW/ACT, who have vocally opposed the changes since they were leaked to the media more than a week ago, said the passing of the legislation late last night marks the "beginning of a major campaign that will not end until the laws are scrapped".

ALS chief executive Karly Warner, who has labelled the laws a "a devastating betrayal of Aboriginal children in NSW," said the organisation was "drawing a line in the sand".

"We cannot accept an Australia that puts children in jail instead of evidence-based policy that actually makes communities safer," Ms Warner said.

An open letter signed by ALS NSW/ACT, the NSW Bar Association and Amnesty International Australia along with 500 academics, advocates, lawyers, and health experts have voiced their opposition to the government's bail plans, but they were passed last night in an extended sitting.

​"Time will show that these laws will increase crime and make communities more dangerous," Ms Warner said.

"We won't stop until this betrayal of vulnerable children and of Closing the Gap is overturned and replaced with the solutions that actually make a difference.

"This is the beginning, not the end, of our advocacy."

Greens MP and spokesperson for justice Sue Higginson said the laws were the "legislation of a coward."

"The opposition to these laws is remarkable," Ms Higginson said.

"The Bar Association, the Law Society, the cross bench and even members of the Liberal Party and the government united against both the spirit and execution of new laws.

"We've witnessed unanimous, grave concern about the careless breadth and consequences of these laws. This is legislation forced on the government and the state by the Premier to appease a few shock jocks and columnists."

ALS NSW/ACT said they welcomed internal pressure from the Labor party, with the NSW Society of Labor Lawyers penning an open letter calling the laws "not fit for purpose."

The letter, addressed to the State Parliamentary Labor Party (SPLP), said the new legislation was a "band-aid solution, likely to lead to the incarceration of particularly vulnerable groups in our society, which will further entrench criminality in regional communities and strain our criminal justice and prison system".

"While the reforms come with promises of safer communities, the effect will be a short-term sugar hit for regional communities at the expense of long-term safety," it says.

The letter cites Article 37(b) of the Convention on the Rights of the Child, which Australia has ratified which states: "No child shall be deprived of his or her liberty unlawfully or arbitrarily. The arrest, detention or imprisonment of a child shall be in conformity with the law and shall be used only as a measure of last resort and for the shortest appropriate period of time".

"It is difficult for the Society to see how that principle, which is binding on all Australian legislatures under international law, is being respected when this Bill is likely to lead to a child being more likely to be imprisoned on remand than an adult in the same circumstances," the letter said.

Ms Warner said ALS NSW/ACT welcomed the letter and advocacy from legal groups who "know these new laws will be a disaster for regional NSW and for the Labor Party".

"This internal opposition shows that while the Bill has passed, the fight to rectify these dangerous laws is far from over," she said.

Premier Minns has also refused to raise the age of criminal responsibility in NSW from 10 to 14, despite significant evidence from medical and legal groups arguing it needs to be done to ensure child and community safety and ultimately reduce recidivism.

The open letter criticised this, arguing the decision is "directly contrary to the support in principle position that the NSW Labor Conference extended to the raise the age campaign at the 2022 annual conference".