A leading organizer of the pro-democracy protests in Hong Kong appeared in court Tuesday, accused of defying police orders to disband a rally, in what activists say is an effort by city authorities to weaken the opposition movement by deterring others from staging demonstrations.

Ventus Lau, who has organized several large protests over the past few months, was charged with inciting others to take part in an unlawful assembly and refusing or willfully neglecting to obey an order of a police officer.

Police gave Mr. Lau permission for an eight-hour rally on Sunday in the city’s financial district that was attended by thousands of people, but officers at the scene declared it unlawful after 90 minutes, citing violence among some of the participants.

Mr. Lau, a 26-year-old freelance writer, is a spokesman for the Hong Kong Civil Assembly Team, which has organized at least 19 rallies since June. If convicted, he faces up to six years in jail, according to his lawyer.

Fellow activists criticized the arrest of Mr. Lau as the latest sign of tougher police tactics in recent weeks as Hong Kong authorities seek to end seven months of turmoil in the city. Citizens first took to the streets in June to oppose a since-withdrawn extradition bill. The movement has evolved into a broader call for democracy and for police to be called to account for alleged brutality. Mass rallies have sometimes ended in protesters blockading roads and battling with police throughout the months of unrest.