About 30 sex workers led by advocacy group Zi Teng join a rally to mark the fourth International Day to End Violence Against Sex Workers yesterday. The sex workers, all wearing eye masks and chanting slogans, marched to police headquarters to appeal against the ill-treatment they say they receive when vice activities are investigated. A spokeswoman for the group, Elaine Lam Yee-ling, said there had been more than 200 complaints this year from prostitutes claiming abuse of police powers. 'Some officers took advantage of undercover operations to harass sex workers. It included free masturbation services and repeated visits to a brothel to 'collect evidence',' she said. 'The complaints against police officers did not help. Instead, they are harassing the sex workers to prevent them from lodging complaints.' Zi Teng made a list of seven major cases of police abuse of power against sex workers and handed it to police during the demonstration.