A factory worker who helped to organize a strike during China's 1989 pro-democracy protests has been released after nearly 15 years in prison, a U.S.-based prison rights group said Saturday.

Chen Gang (search) reportedly was convicted of "hooliganism" and sentenced to life in prison following the violent crackdown that ended the 1989 protests centered on Tiananmen Square (search) in central Beijing, the Dui Hua (search) Foundation said.

Chen was released in April after the government reduced his sentence several times, the foundation said, citing information it said it had just received from China's Justice Ministry.

The announcement highlighted the detention of people sentenced to long prison terms after the 1989 crackdown. It wasn't clear how many were still behind bars on charges of counterrevolution.

Chen worked for the Xiangtan Electrical Machinery Plant, one of the biggest government factories in the central province of Hunan, the Dui Hua Foundation said. It said he helped to organize a strike that shut down the factory during the 1989 protests.

Communist leaders were especially severe in punishing such labor activists after the 1989 crackdown, apparently fearing that unrest among China's vast urban working class was a grave threat to party control.

The San Francisco-based Dui Hua Foundation researches Chinese prisons and has been involved in securing the release of dozens of prisoners. Its director, John Kamm, was among 23 recipients this year of prestigious "genius grants" by the John D. and Catherine T. MacArthur Foundation.