An adviser to the House Committee on Law on Tuesday filed a complaint with police against protest leader Jatuporn Prompan for allegedly violating the lese majeste law.
Sonthiya Sawasdee, adviser to the House committee on law, justice and human rights, on Tuesday asked police at Chana Songkhram station to look into Mr Jatuporn's speech that he delivered on Sunday at the Santiporn Park on Ratchadamnoen Road -- where he held a mass protest for the Sammakhi Prachachon Pheu Prathet Thai (People's Unity for Thailand) -- to see if it violated the lese majeste law.
The protest was held to demand the resignation of Prime Minister Prayut Chan-o-cha.
Mr Sonthiya said he believed Mr Jatuporn's speech violated the lese majeste law but added that it was up to the police to decide whether or not to press charges against him.
The authorities enforced the lese majeste law out of good intentions to create peace in the country, he said.
Mr Jatuporn, who is also chairman of the United Front for Democracy against Dictatorship (UDD) -- popularly known as the red shirts -- has a constitutional right to protest against anyone. However, he must not disrespect the monarchy as Thai people cannot accept it, the adviser said.
The UDD chairman addressed a rally of about 500 people on Sunday evening at Santiporn Park. The rally began at about 4pm and ended later in the evening.
Mr Jatuporn said the campaign would continue, with daily rallies planned at the park to call for Gen Prayut's removal from office.
"The 2017 constitution is Thailand's worst, and it is Gen Prayut who has benefited the most from it," he said.
Among those in attendance at Sunday's rally were Pibhop Dhongchai, a former core member of the People's Alliance for Democracy (PAD); Veera Somkwamkid, secretary-general of the People's Anti-Corruption Network; Karoon Sai-ngam, a former Buri Ram MP; Taikorn Polsuwan, a former leader of an anti-Thaksin group; and Saknarong Mongkol, a law professor at Thammasat University.