HONG KONG — The police in Beijing have formally arrested a prominent Chinese businessman who turned his energies and wealth to supporting human rights causes, his lawyer said on Monday. The arrest of the businessman, Wang Gongquan, was another step in the Communist Party’s drive to deter dissent, supporters said. Notice of the decision comes a day before China is scheduled to defend its human rights record at a United Nations hearing.

Mr. Wang’s lawyer, Chen Youxi, said in a brief telephone interview that a police officer had called him to say that on Sunday Mr. Wang had been formally arrested on charges of “assembling a crowd to disrupt order in a public place.” Mr. Wang was detained on the same charges last month, and the decision to formally arrest him will give the police more time to hold him and to build a case, on that or other charges.

Mr. Chen later wrote on a popular Chinese microblogging site, Sina Weibo, that Mr. Wang’s family had received the arrest notice, and he posted an image of the notice. Calls to Mr. Wang’s wife, Cao Yuping, were not answered. Officers at a detention center in Beijing where supporters have said Mr. Wang is being held would not answer any questions.

Mr. Wang, who turns 52 on Tuesday, is an unusually prominent and established target for Chinese police officers seeking to stifle political activism: a wealthy venture capitalist who made a fortune investing in real estate, high-tech firms and other ventures.