HANOI (Reuters) - A court in northern Vietnam on Thursday sentenced an activist to 20 years in prison after he was convicted in a one-day trial of attempting to overthrow the state, his lawyer said.

The People’s Court in Nghe An province also sentenced Le Dinh Luong, 53, to five years house arrest to be served after his prison term, lawyer Ha Huy Son said.

“The court charged him with activities “aimed at overthrowing the people’s administration” but they didn’t have sufficient evidence,” Son told Reuters on the phone.

“Luong didn’t plead guilty at the trial and he will appeal the verdict,” he said.

Despite sweeping economic reform and increasing openness to social change, Vietnam’s ruling Communist Party retains tight media censorship and does not tolerate criticism.

State media cited police in the province as saying Luong is a “dangerous” member of the U.S.-based human rights group Viet Tan, which Vietnam regards as a “terrorist” body.

Luong, arrested last year, encouraged people to boycott a National Assembly election in 2016, incited protests against Taiwanese steel firm Formosa and wrote posts on his Facebook account that expressed views against the party and the state, reported the communist-party-run Nghe An newspaper.

Taiwan’s Formosa Plastics Corp was blamed for causing one of Vietnam’s worst environmental disasters in 2016, when a steel plant being developed by the company contaminated coastal waters, unleashing anger throughout the country.

New York-based Human Rights Watch late last month called on Vietnam to drop charges against Luong, saying the charges are politically motivated.

“Le Dinh Luong is facing prison for protesting the dumping of toxic waste and other environmental disasters that the government should be doing something about,” Phil Robertson, deputy Asia director at Human Rights Watch, said ahead of the trial.

Luong’s trial came two months after Vietnamese legislators approved a cybersecurity law that tightens control of the internet and global tech companies operating in the country, raising fears of economic harm and a further crackdown on dissent.

In June, Vietnam deported human rights lawyer Nguyen Van Dai to Germany, two months after he was convicted of attempting to overthrow the state and given a 15-year jail sentence.