The Constitutional Court ruled on Wednesday that three activists aimed to overthrow the state and the monarchy in their speeches, and ordered them and other parties to end all moves against the highest institution.
The court said Arnon Nampa, Panupong "Mike" Jadnok and Panusaya "Rung" Sithijirawattanakul attempted to overthrow the democratic institution with the King as head of state in demands made during a rally at Thammasat University Rangsit campus on Aug 10, 2020 and on other occassions afterwards.
The activists listed 10 demands in their manifesto delivered at Thammasat and at subsequent events, includng a call for reform of the monarchy and the abolition of Section 112, known as the lese majesty law.
The judges ruled that these demands were in violation of Section 49 of the constitution.
The court also ordered the three respondents and others to end their movement.
"The three respondents, other organisations and networks must cease their actions," the judges said in their ruling, read out at the court on Wednesday afternoon.
The court said the ruling carried no penalty for the three respondents.
Only Ms Panusaya was at the court. Mr Arnon and Mr Panupong sent representatives to hear the ruling. They all refused to stay in the courtroom and waited outside.
The court was ruling on a petition filed by Natthaporn Toprayoon, a former adviser to the Ombudsman, on Sept 3 last year. He asked the court to decide whether the activists' demands were in violation of Section 49.
"No person shall exercise the rights or liberties to overthrow the democratic regime of government with the King as Head of State," the unofficial translation of the section reads.
He named eight people in the petition - including Parit "Penguin" Chiwarak, Juthathip Sirikhan, Siripachara Jungteerapanich, Somyot Prueksakasemsuk and Artitaya Pornprom, who spoke at other rallies.
The court decided later that only Mr Arnon, Mr Panupong and Ms Panusaya were involved in the incidents cited in the petition.
All parties involved, including public prosecutors, police, other security authorities, the university and the three protest leaders were ordered to submit evidence to the court.
The three leading protesters said in a closing statement as part of the evidence sent to the court that they had no intention to overthrow the highest institution. Their demands were intended to strengthen the constitutional monarchy, the statement said.
The court decided on Sept 27 this year that the petition contained grounds for consideration.
Mr Natthaporn told BBC Thai earlier that the ruling could be used as a basis for authorities working cases against them and other activists and their supporters, including academics and political parties.
In February, he filed a complaint seeking the dissolution of the Move Forward Party on grounds that members' actions were considered hostile to a democratic institution with the King as head of state.
The court premises were declared off-limits on Wednesday, but supporters of the activists gathered beyond the off-limits areas near the court for the reading of the ruling.
Related story: Panusaya, protest group deny attempt to overthrow monarchy