BEIJING (Reuters) - Beijing authorities on Friday took outspoken rights lawyer Yu Wensheng into custody as he was taking his child to school, his wife told Reuters, days after Yu said he was stripped of his legal license for criticizing President Xi Jinping.

Yu, a Beijing-based lawyer and activist, has repeatedly criticized the ruling Communist Party over a sweeping crackdown on rights lawyers and activists, which has seen hundreds detained and dozens arrested in recent years.

The authorities revoked Yu’s license on Monday, citing rules requiring he be employed at a registered firm, but Yu told Reuters he believed the decision was in part reprisal for an open letter he wrote criticizing Xi’s “totalitarian” rule.

Early on Friday morning, as Yu was taking his child to school, he was stopped by a squad of four police vehicles and over 10 officers, and taken into custody, Yu’s wife Xu Yan told Reuters.

“I have not received any legal document about his detention and don’t even know what crime he is suspected of committing,” she said.

Xu added that she is in the process of searching for a lawyer to defend Yu if necessary, but many of those lawyers she knows in Beijing also have problems with their licenses.

It is unclear where Yu is being held and if he has been charged with any crime. China’s ministry of public security did not immediately respond to a request for comment.

On Thursday, Yu released another open letter calling for changes to China’s state constitution to make elections fairer, reduce military power and delete a preamble that gives the Communist Party primacy in national leadership.

Yu had been involved in a number of high-profile and politically sensitive cases, including defending fellow veteran human rights lawyer Wang Yu, following her detention in the summer of 2016.

Yu was detained briefly in October 2017 during a meeting of China’s top leadership after he wrote a letter in which he said Xi was unsuited to rule China and calling for his replacement.

Most recently, Yu had been attempting to defend another detained rights lawyer, Wang Quanzhang, but the authorities have barred him from meeting Wang.

Wang was detained 920 days ago and his case has yet to come to trial. Neither his wife or any of the lawyers that she has asked to defend Wang, including Yu, have been able to meet with him since.