When President Donald Trump visits the coastal city of Da Nang, Vietnam  later this week for the 2017 Asia-Pacific Economic Cooperation meeting, he will undoubtedly send out his thoughts to his tens of millions of Twitter followers. In doing so, he will commit an act that is extremely dangerous for many Vietnamese citizens – using social media.

The space for online dissent in Vietnam is quickly shrinking and the  consequences for those who dare to use social media to criticize the government can be dire. Vietnamese authorities regularly use a series of articles in the Penal Code that criminalize freedom of expression and association to hand down harsh sentences. In a further erosion of online security, in June 2016, a new cybersecurity law came into effect which allows government agencies to request users’ personal information without consent, mandates that authorities be given decryption keys on request, and introduces licensing requirements for tools with encryption as a primary function.

Although the imprisonment of bloggers and online activists is not a new trend in Vietnam, after the collapse of the Trans-Pacific Partnership agreement, the pace of politically motivated imprisonments drastically increased. Since 2016, at least 34 bloggers and activists have been arrested and imprisoned.

Some of these activists are well known, such as Nguyen Ngoc Nhu Quynh, a blogger and the Coordinator of the Vietnamese Bloggers Network. Since 2006, she has been blogging under the pseudonym of Me Nam (Mother Mushroom). She is known for her criticism of the government and has revealed corruption cases and human rights violations committed by the authorities. As a result, she has repeatedly been targeted for harassment, including being arrested and physically attacked. Mother Mushroom was arrested in October 2016 and charged under Article 88 of the Penal Code with “conducting anti-state propaganda.” After nine months in pre-trial detention, she was sentenced to 10 years in prison. In March 2017, the U.S. State Department awarded her the International Woman of Courage Award at a ceremony presided over by First Lady Melania Trump.

Other individuals are less well known, such as Nguyen Huu Quoc Duy, an online activist currently serving three years in prison for a Facebook post. Duy was arrested on August 28, 2015, the same day as police arrested his cousin Nguyen Huu Thien An, an active member of a youth movement, who was apprehended spray painting an anti-government slogan on the side of a police station. Before his arrest, Duy was active on Facebook where he made statements and reposted articles criticizing governmental corruption, acts of police violence, and deficiencies in the local educational system on his personal page.

Duy is not a member of the youth movement his cousin was a part of, but was arrested regardless and released three days later.  Almost immediately upon his release, Duy posted on Facebook calling for the release of his cousin. As a result, Duy was arrested again on November 21, 2015 and held incommunicado for nine months during which time he was unable to communicate with his family or a lawyer of his choosing. Once the trial finally began in August 2016 it was closed to the public. Duy was convicted under Article 88 of the Penal Code for spreading anti-government propaganda and sentenced to three years in prison. Following the trial, he was immediately placed in a solitary cell. His mother was unable to visit him until February 2017—15 months after his initial arrest.

When President Trump arrives in Da Nang later this week he should not only call for the release of Nguyen Ngoc Nhu Quynh, Nguyen Huu Quoc Duy, and all political prisoners in Vietnam, but he should also urge Vietnam to end its crackdown on internet freedoms. Maybe he can even do it in a tweet.