Authorities in Beijing on Friday detained a prominent human rights lawyer after he penned an open letter to the ruling Chinese Communist Party about proposed constitutional changes.
Yu Wensheng was taken away from his Beijing home on Friday morning by around a dozen police officers.
His family received a call some 10 hours later informing them that he is being held at the Gucheng police station on suspicion of "obstructing public duties."
Yu's wife said she had gone immediately to the police station to inquire after her husband.
"They came and detained him on Friday morning because he sent out [an open letter] on the 18th," Xu told RFA. "The constitution protects the rights of citizens to freedom of expression, to make suggestions, and his suggestion letter fell within those rights, and fell within the law."
"But in mainland China, they don't let people speak out, and that's why he was detained," she said. "Of course he has done a lot of human rights work in the past three years, which probably also has something to do with it."
Guangdong-based rights lawyer Wang Qingying said he is concerned that Yu will be held under criminal detention, paving the way for a criminal case against him.
"I have a sense that Yu Wensheng is in a lot of danger right now; that they will detain him for at least a month this time," Wang said. "A lot of people went to detain him, which clearly indicates a criminal detention."
"If they just wanted to talk to him, they would have just sent one or two people over, or just called him up by phone to tell him to come in," he said. "They wouldn't send all those police officers over to take him away suddenly like that. That's why I'm very worried."
'We are pretty worried'
Rights lawyer Liang Xiaojun, who accompanied Xu to the police station earlier on Friday, agreed.
He said Yu's family are trying to get him a meeting with a defense lawyer.
"We are pretty worried," Liang said.
Yu, 51, has defended a number of clients in politically sensitive human rights cases in recent years, including forced evictees and the families of victims of a tainted vaccinations scandal in the eastern province of Shandong.
In 2014, he was held by police for 99 days for showing public support for the pro-democracy Occupy Central movement in Hong Kong.
Yu was stripped of his professional license to practice after he joined the defense team for detained fellow lawyer Wang Quanzhang, held in the northern city of Tianjin amid a nationwide crackdown on lawyers and rights activists that began in July 2015.
Reported by Wen Yuqing for RFA's Cantonese Service. Translated and edited by Luisetta Mudie.