The crackdown has extended to lawyers such as Xu Zhiyong. He said Beijing authorities have held him under informal house arrest since mid-October, stationing four or five guards outside his apartment in Beijing around the clock.
Xu has campaigned for years against Chinese authorities' use of "black jails," or unofficial detention centers run by local governments to hold petitioners. The government has denied the existence of such facilities, but even the tightly controlled state media have reported on them.
"The illegal restriction of a citizen's personal freedom for a long period of time is criminal behavior," Xu wrote in an email. "In an authoritarian state, this type of crime takes place everywhere."
Authorities in Shanghai also have ratcheted up pressure on critics, sentencing veteran women's rights activist Mao Hengfeng to a year and a half of labor camp. Mao, accused of disturbing social order, had been detained in Beijing in late September, said her husband, Wu Xuewei, who indicated she was being put away to silence her before the party congress.
Even dissidents' relatives have come under pressure. Beijing activist Hu Jia said he was warned by police to leave town, and that even his parents told him that police had told them to escort him to his hometown.
"My parents said to me: 'Hu Jia, you don't know what kind of danger you are in, but we know,'" he recounted in a phone interview from his parents' home in eastern Anhui province. "They said: 'Beijing is a cruel battlefield. If you stay here, you will be the first to be sacrificed. Don't do this.'"