Reporters Without Borders charges the Internet giant with providing information that helped put a local writer in jail.
A French media watchdog group claimed on Tuesday that Yahoo provided information that helped Chinese officials convict a journalist accused of leaking state secrets.
Shi Tao, a 37-year-old writer for the Dangdai Shang Bao (Contemporary Business News), was sentenced in April to 10 years in prison, Reporters Without Borders said in a statement. He was convicted of sending to foreign Web sites a "top secret" government message that had been sent to his newspaper.
The international watchdog organization said recently translated court papers revealed that Yahoo Holdings in Hong Kong provided Chinese investigators with detailed information that helped them link Shi's personal e-mail account and a specific message containing the "state secret" to the IP address of his computer.
The state secret was a message to Shi's newspaper warning journalists of the dangers associated with dissidents returning to mark the 15th anniversary of the Tiananmen Square massacre, according to the group. Shi admitted sending the e-mail but disputed whether it was a secret document.
"We already knew that Yahoo collaborates enthusiastically with the Chinese regime in questions of censorship, and now we know it is a Chinese police informant as well," Reporters Without Borders said in its statement.
The Sunnyvale, Calif.-based company responded to the charges in a written statement: "Just like any other global company, Yahoo must ensure that its local country sites must operate within the laws, regulations and customs of the country in which they are based."
The harsh criticism comes as Yahoo and rivals Microsoft and Google are engaged in a high-stakes fight to expand into the lucrative Chinese marketplace.
Just last month, Yahoo paid $1 billion for a 40 percent stake in Alibaba.com, which many consider to be the largest e-commerce company in China. Meanwhile, Google and Microsoft are fighting in a Washington state court over the , a former Microsoft employee who helped the software giant build up its Chinese offices. Google hopes Lee will help expand its presence in China as well.