The kingdom has seen near-daily demonstrations for weeks by mostly young students denouncing the military-aligned government of premier Prayut Chan-O-Cha. 

Anon Numpa, a 35-year-old human rights lawyer, and another activist were arrested Friday and charged with sedition and breaking coronavirus rules for taking part in a Bangkok rally last month. 

The arrests also came four days after Anon led a discussion at a subversive protest on the monarchy's role in Thailand.

Released on bail on condition they would not repeat the alleged offences, Anon travelled Sunday to Chiang Mai, a northern city popular with tourists, to speak at a rally. 

"We repeat our three demands: stop threatening the people, dissolve the parliament and write a new constitution," he told a cheering crowd of roughly 400. 

Analysts say the 2017 military-scripted charter tipped the scales of last year's election in favor of former army chief Prayut and his party. 

Protesters regard his administration -- stacked with ex-generals and elite establishment allies -- as a legacy of a royalist junta regime.

"We call for this charter to be amended because it is the inheritance of dictators," said Anon 

His speech avoided the discussion of reforming the kingdom's draconian royal defamation laws, which protects the monarchy from criticism. 

The law carries a sentence of up to 15 years per charge, making open scrutiny of the super-rich King Maha Vajiralongkorn virtually impossible. 

No charges have so far been filed under the law against the protesters.

Another anti-government protest expected on Sunday in Phitsanulok province was cancelled, according to its organizer on Facebook, who announced it under the hashtag "stop threatening people". 

Protesters say their nascent pro-democracy movement has been organized organically, with young leaders taking to social media to promote the flashmobs. 

The coronavirus pandemic has sent Thailand's economy into freefall, sharpening the discontent of young Thais as the downturn laid bare the equalities of a society perceived to favor the elite, pro-military establishment.