Vietnamese human rights activists and independent media groups have written to Mark Zuckerberg, Facebook Inc.'s chief executive, questioning whether the social media platform was helping suppress dissent in the communist country.

The letter, released on Tuesday by U.S.-based human rights group Viet Tan and signed by nearly 50 other groups, said Facebook's system of automatically pulling content if enough people complained could "silence human rights activists and citizen journalists in Vietnam."

Despite sweeping economic reform in Vietnam, and increasing openness toward social change, including gay, lesbian and transgender rights, the ruling Communist Party retains tight media censorship and does not tolerate criticism.