Protesters were gathering Saturday in Bangkok for the most ambitious rally so far in a pro-democracy campaign that has shaken up the government and Thailand's conservative establishment.
Organisers are predicting as many as 50,000 will show up and march over two days in an area of the capital historically associated with political protests.
An estimated 10,000 people turned out for the last major rally on August 16, and this time, opposition political parties are expected to join and mobilize supporters from other provinces.
Demonstrators ignored a Thursday night plea from Prime Minister Prayuth Chan-ocha to cancel the event, which he said risked spreading the coronavirius and derailing recovery of the battered economy.
The core demands declared by the protesters in July were the dissolution of parliament with fresh elections, a new constitution and an end to intimidation of political activists.
They believe Prayuth, who as then-army commander led a 2014 coup toppling an elected government, was returned to power unfairly in last year's general election because the laws had been changed to favor a pro-military party.
A constitution promulgated under military rule is likewise undemocratic, they charge.
The mostly student activists raised the stakes dramatically during the August 10 rally by issuing a 10-point manifesto calling for reforming the monarchy.
Their demands seek to limit the king's powers, establish tighter controls on palace finances and allow open discussion of the monarchy.
Their boldness was virtually unprecedented, as the monarchy is considered sacrosanct in Thailand, and any criticism is normally kept private.