Police have summoned five organisers of student-led protests against the government, saying they had violated a coronavirus emergency decree that forbids large gatherings, a senior officer told Reuters on Wednesday.
Among those called for questioning was human rights lawyer Anon Nampa, who two days ago had demanded reforms of Thailand's powerful monarchy, a highly sensitive topic.
Police said, however, Mr Anon, 35, was being summoned over an earlier protest in July outside the army headquarters.
That demonstration was among a series of near-daily, student-led rallies around the country since mid-July that have demanded the resignation of Prime Minister Prayut Chan-o-cha and amendments to a military-drafted constitution they say maintains army influence over the political system.
"Anon and four others have been summoned for questioning and to hear the charge of breaching the emergency decree," Pol Lt Col Athich Donnanchai, deputy superintendent of Nanglerng police station, told Reuters.
Mr Anon was separately the subject of an official complaint on Wednesday that asked police to take action against him for breaches of the emergency decree and of the constitution, concerning his remarks about the monarchy.
Defaming the monarchy is punishable by up to 15 years in prison under Thailand's strict lese majeste law, which Mr Anon had also criticised.
Police said they were looking into what took place at Monday's protest, where Mr Anon was a key speaker.
Asked about his summons, Mr Anon in a text message said the decree "is a law to gag and stop activism".
The government last month said the emergency decree in place since March would only be used as a measure against the coronavirus and from August onwards said it would not be used to prevent political rallies.
Six protest leaders or political activists in two different provinces were summoned last month for breaching the emergency decree, among other alleged offences.
In remarks at a military academy on Wednesday, army chief Apirat Kongsompong made no specific mention of the protests, but told military cadets they must be loyal to the nation.
"(Covid-19) is a curable disease, but hating the nation, hating one's own country, this a disease that is not curable," Gen Apirat said.