The police have refused to grant the Civil Human Rights Front permission for a rally and march planned for this Sunday, saying there is reason to believe participants would deviate from the suggested route, damaging buildings and threatening the safety of the general public.
A letter from the force says the rally planned in Causeway Bay is therefore "banned", while the police are "objecting" to the plan to hold a march from Causeway Bay to Central.
The police say there has been "chaos", "violence", "road blockages" and "destruction" following previous marches organised by the front, and the organisers would not be able to control those joining the planned protest.
They also say the proposed route for the march would pass close to high-risk buildings including the police's headquarters in Wan Chai, Government House in Central, and several MTR stations.
Police have banned a number of protests in recent weeks, with most of them going ahead regardless.
The Civil Human Rights Front have been responsible for some of the bigger protests this summer, including the peaceful marches on Hong Kong Island attended by hundreds of thousands of people.
The group's vice-convenor, Bonnie Leung, said the ban will only make people even more angry, and some even more radical.
"If peaceful protests don't work, or are not permitted at all, it's human nature that people will go more and more radical, people will escalate their action. It is like declaring war on even the most peaceful protesters," she said.
Leung added that the front is appealing against the ban.