BEIJING — Two prominent human rights lawyers have lost their licenses after volunteering to defend Tibetans charged in the violent anti-China protests that erupted in March. The decision comes as Chinese authorities are tightening scrutiny over dissidents in advance of the Olympics in August.

The two lawyers, Teng Biao and Jiang Tianyong, are known for taking on politically contentious cases, including those alleging official abuses of human rights. Reached on Tuesday night, Mr. Teng said he learned last week that judicial authorities had renewed the license of every lawyer in his firm, except his own.

“Obviously, it is because of the Tibetan letter that I signed and also other sensitive cases I handled,” Mr. Teng said.

Judicial authorities could not be reached for comment on Tuesday. But human rights groups say the authorities initially considered denying license renewals for numerous lawyers, only to relent in the cases other than those of Mr. Teng and Mr. Jiang.

Lawyers are increasingly at the cutting edge of efforts to push systemic change in China. Self-styled “rights defenders” regard the law as a tool to expand and protect the rights of individuals in an authoritarian political system. But the ruling Communist Party is often wary of lawyers who try to challenge what it regards as the unassailable pre-eminence of the party in society.

In April, 18 lawyers signed a public letter volunteering free legal services to Tibetans arrested during an official crackdown against protests in western China. State media reported that 30 Tibetans, represented by government-appointed lawyers, were given sentences from three years to life during trials in April. Mr. Teng said the judicial authorities were not pleased with the offer of free legal counsel and later warned the lawyers not to get involved in the Tibetan situation.

By May, Mr. Teng said, his law firm applied for its standard annual renewal of licenses. But the firm’s licenses were suspended. “They just informed my boss that I was the reason the whole firm was in trouble,” Mr. Teng said. But on Thursday, the authorities lifted the suspension and granted renewals for the other 60 or so lawyers in the firm.

Last month, before a final decision had been made on the licenses, Mr. Jiang said his status was in jeopardy because of his willingness to handle “sensitive cases.” “As a lawyer, I only care about whether the case can be legally defended,” Mr. Jiang told The South China Morning Post in Hong Kong. “I will follow the right rules within the law. I don’t know how to judge whether a case is sensitive or not.”