BANGKOK (AP) — A prominent Thai human rights lawyer was convicted on Tuesday of insulting the monarchy and sentenced to four years in prison, the first conviction under a controversial law guarding the royal institution since a civilian government took office after years of military-backed rule.

Arnon Nampa was found guilty of defaming King Maha Vajiralongkorn during a student-led rally on Oct. 14, 2020, that commemorated a popular uprising in 1973 that led to the fall of a decade-long military dictatorship. He was also fined 20,000 baht ($550) for violating an emergency decree banning large public gatherings during the coronavirus pandemic.

Arnon, 39, still faces 13 more cases under the lese majeste law, which makes insulting the monarch, his immediate family and the regent punishable by up to 15 years in prison.

The court said in its ruling Tuesday that Arnon had declared at the rally that if it were dispersed, it would be at the order of King Maha Vajiralongkon. It said that statement was false because such actions would be up to the police to decide, and that Arnon had therefore defamed the king.

Arnon’s lawyer, Kritsadang Nutcharat, said his client will appeal and seek bail. Arnon hugged his son before being taken away to be jailed.

Arnon told reporters before entering the courtroom that even if he loses his freedom, his struggle is worth fighting for. He was accompanied by his wife, son and father. About 20 other people came to Bangkok Criminal Court to express their solidarity.

“The movement of the new generation created a phenomenon of change for the country in a way that cannot be turned back,” Arnon said. “I want the fight of the new generation to truly change the country.”

Arnon was awarded the 2021 Gwangju Prize for Human Rights by a South Korean foundation for his pro-democracy work.

He was among the first people to publicly call for reform of the monarchy and has remained one of the most vocal advocates of the movement. Earlier this year he accused the government of using internationally notorious Pegasus spyware to monitor his mobile devices.

The monarchy has long been considered a pillar of Thai society and criticism of it has been taboo. Conservative Thais, especially in the military and courts, still consider it untouchable. However, public debate on the topic has recently grown louder, particularly among young people.

Critics say the lese majeste law is often used to quash political dissent. At least 257 people have been charged in 278 cases since November 2020, including at least 20 minors, according to the group Thai Lawyers for Human Rights.

Opposition to reform of the monarchy was highlighted after Thailand’s general election in May which ended the nearly decade-long rule of Prayuth Chan-ocha, who initially took power in a 2014 military coup.

The progressive Move Forward Party won the most seats in the election but was denied power by Parliament. Conservative members of the military-installed Senate, which picks the prime minister together with the elected House of Representatives, voted to block party leader Pita Limjaroenrat from taking the post, citing his party’s call for a mild reform of the lese majeste law.

The populist Pheu Thai party, which ran second in the election, then formed a coalition with military-backed parties and succeeded in forming a new government led by Prime Minister Srettha Thavisin. Pheu Thai pledged not to touch the lese majeste law to win support for its rule.