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.

Vietnam last year unveiled a 10,000-strong military cyberwarfare unit, named Force 47, to counter “wrong” views on the internet.

The open letter to Zuckerberg called Force 47 “state-sponsored trolls” whom it accused of exploiting Facebook’s community policies and disseminating fake news about the activists.

“Our community standards, which outline what is and isn’t allowed on Facebook, seek to encourage expression and create a safe community on the platform,” a Facebook spokeswoman said in response.

“We will remove content that violates these standards when we’re made aware of it,” the spokeswoman added, in an email statement which said the company’s policy in Vietnam was in line with that elsewhere.

“There are also times when we may have to remove or restrict access to content because it violates a law in a particular country, even though it doesn’t violate our community standards,” it added.

Vietnam’s foreign ministry did not offer any immediate comment on the letter.

Vietnam previously said Facebook had committed to work with the government to prevent illegal content from appearing on its platform and would also remove fake accounts and fake content about senior government officials.

Activists said the frequency of takedowns had risen and Facebook had been unhelpful in restoring accounts and content, after its Head of Global Policy Management Monika Bickert met Vietnam Information Minister Truong Minh Tuan in 2017.

Vietnam’s government cited Facebook as having said at the time of the meeting that it would set up a separate channel to directly coordinate with the communication and information ministry on reports of illegal content.

Facebook’s process and policies for government requests did not change as a result of the meeting, the firm said on Tuesday.

“We appreciate Facebook’s efforts in addressing safety and misinformation concerns online in Vietnam and around the world,” the activists said.

“Yet it would appear that after this high-profile agreement to coordinate with a government that is known for suppressing expression online and jailing activists, the problem of account suspension and content takedown has only grown more acute.”

Vietnam this month jailed human rights lawyer and activist Nguyen Van Dai for 15 years on the charge that he “aimed at overthrowing the people’s administration,” with six more activists jailed for seven to 13 years.

Their sentences prompted responses from representatives from the United States, the United Kingdom, Germany, the Netherlands and the European delegations and rights groups.

Foreign ministry spokeswoman Le Thi Thu Hang said, “There is no such thing as people being arrested for freely expressing opinion” in Vietnam, however.