Student activists have lodged a complaint to the police watchdog, accusing officers of abusing their power at a recent protest.
A woman who took part in the demonstration said she was grabbed from behind by a male officer, who touched her breasts in the process while a woman officer stood nearby.
The activists have been asking police to make public the guidelines covering the circumstances in which male officers can be sent to handle women protesters.
About 10 activists submitted a petition to the civilian-run Independent Police Complaints Council (IPCC), led by Federation of Students secretary general Eddie Chan Shu-fai.
"We are students and we have no weapons," Chan said. "There is no reason for the police to use force. We fear it may be a tactic by the police to scare off people so no one will dare to stage protests in the future."
About two dozen students demonstrated at a ceremony attended by Chief Executive Leung Chun-ying at the Caritas Institute of Higher Education in Tseung Kwan O earlier this month.
Protesters occupied a street, blocking Leung's car. They demanded he meet them to discuss universal suffrage. After a 20-minute stand-off, officers carried the students away.
Ho Kit-ming, a student at the institute, said later that as she tried to approach Leung's car, an officer grabbed her from behind. She discovered it was a man only the next day when she saw a newspaper picture.
IPCC secretary general Ricky Chu Man-kin, who received the petition, said his council would refer the case to the police force's internal complaints investigation unit - the Complaints Against Police Office - to follow up.
Meanwhile, student activist group Scholarism said police breached the mutual trust between them in their march on Sunday to call for the vindication of June 4, 1989, victims.
Group convenor Joshua Wong Chi-fung said they had informed and liaised with police about the march, including its route and number of participants, in the seven preceding days. "Police showed no objection to any of the arrangements in all the seven days of co-ordination," he said.
But the police "unilaterally breached collaboration" when they told the organisers half an hour before the march that they could use only the pedestrian paths.