When police arrested actor Huang Haibo for hiring prostitutes in Beijing, his detention stretched out to six months as the authorities sought to change his bad conduct.

Huang was given half a year of "custody and education", a little known penalty reserved for offenders in sex-related cases. With "re-education through labor" having been scrapped, the semi-official detention has stirred controversy.

Huang's colleagues published an apology on Weibo, stating that Huang "would not protest or sue" in the hope of securing his early release - to no avail.

"Custody and education" can see offenders detained from six months to two years while they are taught about sex-related laws and ethics, serve as laborers, and are tested and treated for sexually transmitted diseases.

Local public security departments have jurisdiction over the period of detention with no judicial procedures or oversights. The system has also led to allegations of corruption, with stories of detainees and their families paying the police for early release.

Huang's case could prompt a review of "custody and education" or even see an end to the system, said professor Qi Dongwen with the law department of Chongqing University of Posts and Telecommunications.

"'Custody and education' is not administered under the law in China," Qi said.

The Law of the People's Republic of China on Penalties for Administration of Public Security allows jailing and fines for sex-related offenses, but not "custody and education", he said.

"Custody and education" also violates the Legislation Law that was enacted to standardize lawmaking activities in China, said Jiang Mingan, director of the Constitution and Administrative Law Research Center of Peking University.

The Legislation Law states that any policies that restrict a person's freedom must be authorized by the Standing Committee of the National People's Congress.

Some NPC deputies proposed scrapping the 20-year-old system at the annual session of the national legislature in March this year. A letter signed by 108 people, including legal experts, was sent to the NPC Standing Committee seeking abolition of the system.

In Guangdong province, a man who was sentenced to six months in "custody and education" for hiring prostitutes sued the public security authorities. A court later determined the man had been sentenced without any evidence.

If the system was abolished, prostitution could be tackled under China's Criminal Law, said Yu Mingyong, a political advisor of Guangzhou.

"Jail and fines already serve to discourage such acts," Yu said.

Xinhua News Agency