Ye Haiyan, 39, had planned to depart for the AIDS 2014 conference in Melbourne on Wednesday, but said she was told she had been placed under a travel ban, meaning she could not board her scheduled flight.

Ms Ye, who lives in Wuhan, is best-known for campaigning for the rights of sex workers including calling for the legalisation of the profession in China, where prostitution is prevalent but illegal.

In 2012, she offered sex for free to impoverished farmers and migrant workers for a day in a run-down brothel. She catalogued her experiences in her highly read blog to highlight the plight of both prostitutes in rural China – some who make as little as $2 a client – and low-income men who are too poor to marry or even maintain relationships.

“I’ve been engaged in this [activism] for nine years, what I’m happiest about has been to see the change in attitude [toward sex work] in civil society,” she told Fairfax Media. “But the government’s attitude in this regard is still unchanged, the issue of sex workers’ rights is still unresolved.”

In Melbourne, Ms Ye was slated to make a presentation on the experiences and rights abuses of Chinese sex workers at sessions preceding the formal conference, which kicks off Sunday and will see former US president Bill Clinton, musician and activist Sir Bob Geldof and thousands of AIDS researchers and community leaders attend.

“An important thing to realise is that a large percentage of this conference’s content and focus is on human rights for affected communities including sex workers,” Janelle Fawkes, the chief executive of the Scarlet Alliance, Australia’s national peak body for sex workers, said. “There’s a focus on the way in which barriers which limit human rights to sex workers … and how that impacts on a country’s HIV responses.”

The International AIDS Society said it was “very concerned” by the decision by Chinese authorities to block Ms Ye from travelling to Melbourne.

“Activists and representatives of key affected populations are a pivotal part of the International AIDS Conference and its program,” it said in a statement. “We therefore ask that the decision to bar Ye Haiyan from travelling be reversed.”

In May last year, Ms Ye again garnered national attention – and the wrath of authorities – when she organised a demonstration against a local school principal and government official accused of raping and sexually assaulting six schoolgirls in a hotel in Hainan.

Ms Ye was physically assaulted in her residence after the protest, evicted from her rental home, and has been harassed consistently since, disrupting her work. Chinese authorities generally have little tolerance for shows of organised dissent and she believes it was the organised demonstration that ultimately led to her being black-listed from overseas travel.

Despite being unable to travel to Melbourne, Ms Ye said she would “continue to have a voice” in advocating for the important changes that need to occur to protect the rights of Chinese sex workers. She said sex workers worried about carrying condoms because police often use them as evidence against them if caught. If sex workers were hurt, they dare not report the crime for fear of revealing their occupation. Sex workers have also become collateral damage, she said, in the government’s politically motivated anti-vice campaign, most prominent in the southern Chinese manufacturing hub of Dongguan.

“The protections available to sex workers are too small, I hope more people will understand,” she said. “I will continue to have a voice. I will continue to tell the government that they are wrong.”

Human Rights Watch’s China director Sophie Richardson said blocking Ms Ye from travelling served to “deny people in China access to the latest thinking and most effective strategies in combating a serious public health challenge”.

“Why wouldn’t the Chinese government want all the help it can get in tackling HIV?” she said.

with Sanghee Liu