"Tang Jingling has been arrested on charges of 'inciting subversion of state power'," his wife Wang Yanfang wrote on her Sina Weibo microblog account, where she also posted a photo of the notice.
Tang, who is being held in the southern city of Guangzhou and who has represented uncompensated victims of land grabs and imprisoned rights defenders, was detained in May on a charge of "causing a disturbance".
Numerous activists were taken in around that time, some temporarily, ahead of the sensitive anniversary of the June 4, 1989 crackdown on pro-democracy protests in Beijing's Tiananmen Square.
Many have faced charges such as disturbing public order or "picking fights and provoking trouble" rather than the more serious charge of state subversion.
"To go from an ordinary crime to now a political crime means it could be more serious," Liu Xiaoyuan, another rights lawyer and acquaintance of Tang, told AFP.
This year several activists from the moderate New Citizens Movement, a loose network in various cities who held small protests against government corruption and other causes, have received jail sentences of up to six and a half years, with most people convicted of disrupting public order.
Chinese activist and 2010 Nobel Peace laureate Liu Xiaobo was in 2009 sentenced to 11 years' jail for state subversion.
He had spearheaded the Charter 08, a document signed by hundreds of dissidents, intellectuals and others urging democratic reforms in China.