Plans to charge licensing fees for brothels in NSW would force many sex workers underground and prevent them from accessing health and welfare services, says the Australian author of a United Nations report.
Human rights lawyer John Godwin's UN report backs the decriminalisation of the sex industry in Asia.
And he says the NSW government's plans to create a brothel licensing authority and charge licensing fees undermines a policy that has been largely successful since its introduction in 1995.
"We currently have a decriminalised sex industry in NSW that has proven to be very successful in terms of both HIV prevention and ensuring a safe and healthy work place for sex workers," Mr Godwin told AAP.
"The licensing systems in the other states have not been evaluated as being highly effective in terms of public health outcomes," he said after the report's launch in Bangkok.
Mr Godwin says the weaknesses of a licensing system are that "it only catches a very small proportion of the industry and the vast majority of sex workers operate outside of licensed establishments".
"Whereas there might be some health benefit for those who are working in the licensed establishments, those who are not are alienated from mainstream services and driven more underground in terms of accessing health and welfare services," he said.
The 226-page UN Development Program report, Sex Work and the Law, calls for decriminalisation of prostitution in Asia, and points to the decriminalisation policy in New Zealand and NSW as enabling sex workers adequate access to services in preventing the spread of the AIDS virus.
The report said the two jurisdictions' approaches indicated that "defining sex work as legitimate labour empowers sex workers, increases their access to HIV and sexual health services associated with very high condom use rates".
"Very low STI (sexually transmitted infection) prevalence has been maintained among sex workers in New Zealand and NSW, and HIV transmission within the context of sex work is understood to be extremely low or non-existent," the report said.
Mr Godwin said it was important to treat the sex industry like any other industry in terms of workplace, occupational health and safety standards.
Instead of a highly bureaucratic and heavy handed licensing system monitoring premises or individual sex workers' there should be application of general and workplace laws as well as zoning requirements for any business, he said.
Tracey Tully, the spokeswoman for the Asia-Pacific Network of Sex Workers, says the NSW policy has been promoted as a model of best practice.
Ms Tully said the policy offers "the most enabling environment legally, in terms of HIV prevention - particularly from key affected populations, which is where the most effective interventions come from".
In Victoria, under a licensed system, operators pay about $A4300 to apply for a brothel licence and $A2500 to renew it. Health workers say the process acts a deterrent for most operators being licensed.