Blind activist Chen Guangcheng (chehn gwahng-chung) says China is violating its promise not to persecute his family.
Speaking before a congressional panel Tuesday, Chen said his nephew has been threatened by Yinan County officials with life imprisonment if he appeals his three-year sentence for assault.
Chen Kegui was sentenced in November in a summary trial, seen as retaliation by local officials angered by his uncle's daring escape from house arrest last April. That set off a diplomatic tussle between Beijing and Washington before the elder Chen, a self-taught rights lawyer, was allowed to leave for America.
The U.S. has said Beijing gave assurances Chen's relatives would be treated in accordance with Chinese law.
Chen says local authorities have also intimidated his nephew's family.