Amnesty International has launched a global campaign against Internet censorship by governments seeking to curtail online freedoms.
In a statement Sunday, the rights group called for the release of dissidents jailed for expressing their political views online.
Amnesty highlights the case of Chinese journalist Shi Tao, who was jailed for 10 years for allegedly providing "state secrets" to foreign entities.
Shi was found guilty of sending an e-mail to a pro-democracy web site in the United States. The note detailed a Chinese government warning to journalists against reporting on pro-democracy activities.
The defendant sent that e-mail through Yahoo, and Amnesty says Yahoo's Chinese partner provided authorities key information that helped convict Shi.
Amnesty also identified Vietnam, Tunisia, Iran, Saudi Arabia and the Maldives as countries where people have been jailed for expressing their views online.
Web search leader Google has come under fire for saying it will block searches on its new China site for material about Taiwan, Tibet and democracy.
Microsoft has been criticized for cooperating with Israel in the prosecution of a nuclear whistle-blower who was ordered not to communicate with foreign journalists.
Yahoo says it condemns all punishments for any activities linked to free expression on the Internet. Google says its presence in China will ultimately force authorities there to ease Internet controls. Some information for this report was provided by AP and Reuters.