A SINGLE thread seems to run through recent detentions and arrests in China: The authorities are cracking down on lawyers and other people who have demanded that China follow its own laws. These advocates have been thorns in the side of the Communist Party for years and were detained for short periods, but now it appears there is a concerted campaign to silence them once and for all.

The latest example has come in the formal announcement on June 13 that a well-respected defense lawyer, Pu Zhiqiang, had been arrested. In May, Mr. Pu took part in a small, private seminar in Beijing where participants discussed the massacre of student demonstrators in Tiananmen Square in 1989. The authorities said his arrest was on charges of creating a public disturbance, apparently a result of his presence at the seminar.

China’s leaders have often rounded up dissidents and others critical of the regime for brief detentions to suppress any displays of discontent on the anniversary of the massacre. Mr. Pu, a hulking presence with a baritone voice, was a student leader during the 1989 protests. A number of people were rounded up again this year; many were subsequently released, but Mr. Pu was not.

It is likely the arrest was related not only to Tiananmen. Mr. Pu, according to the New York Times, has been a crusader known for taking on cases that irritate the party. In recent years, he defended the dissident artist Ai Weiwei as well as victims of the Chinese labor camp system and party members seeking redress for torture they endured during investigations.

Mr. Pu has worked shoulder to shoulder with a corps of lawyers who have devoted themselves to defending rights from within, a subtle approach that is nonetheless aimed at change. China has a legal system with courts and procedures, but the Communist Party and its officials often act above the law. The defense lawyers have represented those whose rights were trampled, attempting to win redress from inside the system by holding China to its own standards.

Chinese human rights lawyer Pu Zhiqiang talks to media in Beijing in this July 20, 2012 picture. (Petar Kujundzic/Reuters)

Even this approach, however, has apparently frightened the party, which holds a monopoly on power in China. Another rights defender, Xu Zhiyoung, a founder of the New Citizens Movement who also sought to hold China to its laws, has been detained since last year. And China is the only nation holding a Nobel Peace Prize winner, Liu Xiaobo, in prison. Mr. Liu championed Charter 08, which called on the state to honor its people’s constitutional rights.

Mr. Pu’s lawyer met with him June 9, a month after Mr. Pu had been detained, and subsequently posted a statement online describing the outlook for his client as “extremely unfavorable.” In China, such arrests often lead to conviction without a genuine trial. China’s president, Xi Jinping, has talked up the notion of a “Chinese dream of national rejuvenation.” But for some like Mr. Pu, even working to uphold China’s existing laws can be a very real nightmare.