BEIJING -- In the five years since it was founded, the Yitong Law Firm has established itself as one of the country's fiercest human rights advocates. It represented Hu Jia, the dissident who spoke out against the Tiananmen Square crackdown and on behalf of HIV/AIDS patients; Chen Guangcheng, the blind activist who exposed forced abortions; and hundreds of others its lawyers felt had been wrongly imprisoned.

Its success rate isn't stellar -- it has won at most 60 percent of its cases. But in a country where rule of law is still a work in progress and calling for democracy is often treated as a crime against the state, Yitong and other human rights firms have spoken out for people who otherwise would have been silenced.

Those days may be over.

Since the beginning of 2009 -- a sensitive year filled with anniversaries of uprisings -- the Chinese government has been forcing human rights law firms such as Yitong to shut down.

Formally, there is no crackdown; no police are swooping in to seize files or send attorneys en masse to labor camps. Instead, Beijing is simply using its administrative procedures for licensing lawyers and law firms, declining to renew the annual registrations, which expired May 31, of those it deems troublemakers. Human rights groups say dozens of China's best defense attorneys have effectively been disbarred.

"It's a collective strike," said Cheung Yiuleung, a leader of the China Human Rights Lawyers Concern Group, an advocacy organization based in Hong Kong. "Compared with individual warnings, the annual check of licenses is more effective. . . . It has had a frightening effect on all lawyers on the mainland."

A few prominent lawyers have met with even harsher treatment. One has gone missing: Gao Zhisheng -- who defended religious minorities such as members of Falun Gong and underground Christians, was a nominee for last year's Nobel Peace Prize and whose family fled China and sought asylum in the United States in March -- was taken by security agents from his home in Shaanxi province Feb. 4 and has not been heard from since.

Several lawyers say they have been beaten en route to meetings with clients in human rights cases. Others have been detained, questioned, put under house arrest for days or weeks and told they must be accompanied by police escorts whenever they leave their homes.

In late May, 17 human rights attorneys whose licenses have been suspended signed an open letter saying authorities are engaging in the "full-scale repression of rights" of defense lawyers "to an unprecedented degree."

With high unemployment from factory closings due to the global economic crisis, China's leaders have expressed concern that the sporadic outbreaks of social unrest in recent months might spread, and they have sought to keep those who might stir up dissent, such as human rights lawyers, under tight rein.

Their concerns are compounded by this year's significant dates: the 50th anniversary of the Tibetan uprising that led to the Dalai Lama's flight to India, the 20th anniversary of the Tiananmen Square massacre, and the first anniversary of protests over the shoddy construction that caused many deaths in last year's Sichuan province earthquake.

Attorneys whose licenses have not been renewed as of this month include Li Xiongbing, who represented victims of contaminated infant formula against the manufacturer Sanlu; Li Chunfu, who has been working on two cases involving wrongful death while in custody; and Wang Yaiun, who fought for the rights of migrant workers who left the countryside to work in urban factories.

Jiang Tianyong, an attorney with the firm Beijing Globe-Law who represents the parent of a child who died during the Sichuan earthquake and Tibetan monks arrested during last year's riots, said he had been warned last year not to take those cases. Representatives of the government's legal affairs bureau came "to talk to me and try to persuade me not to do it. I said, 'Since the law doesn't forbid me, why can't I do that?' "

Because "I don't listen to them and am not controlled," Jiang said, he was not entirely surprised when he learned this month that the renewal of his annual license, typically a formality, had been denied. He said he has been talking to other lawyers in his situation about starting a new, nongovernmental organization or advocacy group so they can continue to help those in need.

Not everyone is as unwavering under government pressure.

Wei Liangyue, head of the Jiaodian Law Firm in the northeastern city of Harbin, said this year was the first time in 21 years his license has not been renewed. In addition, he said, he was detained by police from March 1 to 30, and although he was not given any explanation in writing, he was told he was being punished for taking on Falun Gong clients.

"When I accepted these cases, I already expected the risks. I made my decision for intuitive knowledge and fairness. My decision is right," Wei said. However, he continued, "in the future, I might not touch sensitive cases like this."

Tang Jitian of the Beijing Anhui Law Firm said that the license issue has caused a rift in his office, where some of the lawyers handle human rights cases and others work on less sensitive issues.

"Some lawyers understand us and support us. But some lawyers told the head of the law firm that either we leave or they leave," said Tang, whose license was not renewed and who was detained by police from June 3 to 7 in the basement of a Beijing hotel.

In Yitong's case, managing partner Li Jinsong said authorities ordered the law firm to close for six months starting in mid-March because it employed a lawyer who was not properly licensed. Li called the charge absurd, saying the lawyer held a valid license to practice in another Chinese city and had filed an application to transfer it to Beijing, where the firm is based. Moreover, the penalty -- shutting down the entire firm -- is "100 percent illegal," Li said.

Yitong has appealed the ruling, but it has already had a devastating effect. The firm once attracted some of China's top legal talent -- idealistic men and women in their 30s and 40s, many of whom followed other legal career paths but switched to human rights advocacy because they wanted to make a difference in Chinese society. But now, of the more than 20 attorneys who once worked at its offices, only five are left. The others, concerned about their ability to support their families, took jobs at less controversial firms.

"As a law firm, we must make money. But since we have closed for more than three months, I don't even know if Yitong will still exist," Li said. "I am not sure if we will still have enough money to pay the rent."

Still, Li said he remains determined to take on human rights cases and is hopeful that in the future, lawyers will be able to operate more freely.

"There has to be someone who continues walking on this road. The more people walk, the wider the road will become," he said. "I will fight until I'm beaten to death."