A group of 50 Vietnamese activists and rights organizations have written an open letter to Facebook chief Mark Zuckerberg suggesting his company may be colluding with communist authorities to scrub out online dissent. Activist Nguyen Van Tuc was sentenced to 13 years of prison on Tuesday for posting anti-Communist content online and joining rights groups the government has declared illegal or terrorist, activities that “threaten the survival of the state”. There are at least 97 prisoners of conscience languishing in Vietnamese jails, many of whom are kept incommunicado in squalid conditions and routinely subjected to torture or other ill-treatment, new research by Amnesty International revealed last week.