Reporters Without Borders accused Yahoo of handing over a subscriber's data to Chinese authorities, which resulted in the customer's arrest and imprisonment, an AFP report, quoting an alert released by the media watchdog, said.
Yahoo, however, said it was unaware of the case of Li Zhi, and dismissed what it said were "mischaracterizations" of its past practices in China, the report said.
In an alert cited by the report, Reporters Without Borders said it had discovered new information about the case of Li, whom it described as a cyber-dissident who landed in jail after online politicking.
The group also said it had called on Yahoo to supply a list of all cyber-dissidents subject to data requests from the Chinese authorities, starting with 81 people for whom it was campaigning, the report said.