The Chinese authorities have arrested and charged at least seven human rights lawyers and associates with "subversion", friends and family say.
The employees of Fengrui law firm in Beijing, including founder Zhou Shifeng, have been held in secret since last summer.
If put on trial they may face sentences of between 15 years and life in jail.
China has been conducting a widespread crackdown on activists, including scores of lawyers and their staff.
Mr Zhou came to prominence representing families caught up in China's poison baby milk scandal in 2008. He was detained in July last year - a week later state media reported he had confessed to unspecified crimes.
His colleague, Liu Xiaoyuan, confirmed with the BBC that Mr Zhou, lawyer Wang Quanzhang and intern Li Shuyun had been formally arrested by police under suspicion of "state subversion".
Four others, lawyers Xie Yanyi, Xie Yang and Sui Muqing, and legal assistant Zhao Wei, had been arrested and accused of "incitement to state subversion", AFP news agency reported, citing their friends and relatives.
The BBC's Jo Floto in Beijing says it now looks likely the group will face trial. If they do, conviction is all but guaranteed.
'Public defenders' shut down - Celia Hatton, BBC News
Much has been made of the Chinese authorities' crackdown on defence lawyers. Around 250 lawyers and legal assistants have been detained since last year - a worrying campaign that contradicts Beijing's trumpeted desires to strengthen China's rule of law.
Most of those lawyers have since been released. However, today's formal arrests show that, from the start, the detained lawyers from the FengRui law firm were placed in a different category. Months ago, the firm's offices were completely cleaned out by police.
FengRui was known for taking on high-profile cases that affected large numbers of people, starting with the 2008 baby formula case, when more than 300,000 infants were sickened by tainted formula.
FengRui's lawyers sometimes encouraged petitioners to gather outside the courthouses where their cases were being heard. They took their roles as public defenders very seriously - a move that might have angered the authorities, leading to a comprehensive crackdown that effectively shut down FengRui.
Last year the authorities put out a statement accusing a group led by the Fengrui lawyers of illegally hiring protesters and swaying court decisions in the name of "defending justice and public interests".
It accused the group of organising more than 40 controversial incidents and severely disrupting public order, and gave an example in which it had allegedly presented a legitimate police shooting at a railway station as a murder conspiracy.
In July, the Chinese authorities launched what appeared to be an orchestrated campaign, when more than 280 human rights lawyers and activists - along with their associates - were summoned or detained or just disappeared. The arrests have been widely seen as the state's attempts to stifle dissent.
Last month one of the country's most prominent rights lawyers, Pu Zhiqiang, received a suspended jail sentence after a brief trial for "inciting ethnic hatred" and "picking quarrels" in social media posts.
Rights group Amnesty International called that sentence "a deliberate attempt by the Chinese authorities to shackle a champion of freedom of expression".