A pro-democracy protest expected to draw thousands of young Thais onto the streets this weekend will again demand reform to the country's unassailable and hugely wealthy monarchy, a prominent student leader said Friday.

The kingdom has seen near-daily gatherings from youth-led groups since mid-July demanding a complete overhaul of the administration of Premier Prayut Chan-O-Cha, a former army chief behind the 2014 coup.

Saturday's demonstration is expected to be the biggest since the coup, kicking off at Bangkok's Thammasat University and continuing through Sunday when protesters have pledged to march to the nearby Government House -- a move authorities have warned against.

"We are peaceful, but there could be tension this weekend," Panusaya Sithijirawattanakul, a prominent Thammasat student leader, said Friday.

The kingdom has seen near-daily gatherings from youth-led groups since mid-July demanding a complete overhaul of the administration of Premier Prayut Chan-O-Cha, a former army chief behind the 2014 coup
The kingdom has seen near-daily gatherings from youth-led groups since mid-July demanding a complete overhaul of the administration of Premier Prayut Chan-O-Cha, a former army chief behind the 2014 coup AFP / Lillian SUWANRUMPHA

She vowed that protesters will repeat their call for reforms to the kingdom's ultra-powerful monarchy, a once-taboo topic in Thailand due to draconian royal defamation laws.

"The plan is not to destroy the monarchy but to modernise it, to adapt it to our society," she said.

Sitting at the head of the royal family is the ultra-wealthy King Maha Vajiralongkorn, whose influence permeates every aspect of Thai society.

The kingdom has long seen a cycle of violent protests and coups, with the arch-royalist military stepping in to stage more than a dozen putsches since the end of royal absolutism in 1932.

But the latest wave of student-led demonstrations have been peaceful, while their unprecedented calls for frank and public discussions about the monarchy have sent shockwaves through the kingdom.

Sitting at the head of the royal family is the ultra-wealthy King Maha Vajiralongkorn, whose influence permeates every aspect of Thai society
Sitting at the head of the royal family is the ultra-wealthy King Maha Vajiralongkorn, whose influence permeates every aspect of Thai society THAILAND'S ROYAL OFFICE / Handout

They are also demanding a rewrite to a 2017 military-scripted constitution, which they say tilted last year's election in Prayut's favour, and for the government to stop "harassing" political opponents.

Veteran protest leaders of different political stripes urged restraint from the government on Thursday evening -- a rare show of solidarity from previously warring factions.

"We believe that if the government does not start violence, there will be no deaths," said Jatuporn Prompan, a leader of the so-called "Red Shirts", which supported ex-premier Thaksin Shinawatra.

"When people want political change, they only have one way, which is street protest," said Pipob Thongchai, a former leader of the People Alliance for Democracy -- more commonly known as the "Yellow Shirts", who are pro-royalist and anti-Thaksin.

Authorities have so far arrested more than two dozen student protesters, charging them with sedition before releasing them on bail.

Prayut has in the past warned that Thailand could be "engulfed in flames" if the student movement goes too far.

On Thursday he urged against large gatherings, saying it could increase the risk of a second coronavirus wave in the kingdom.

Thailand has seen a low virus toll, but its tourism-reliant economy has taken a beating due to pandemic border closures.

"Sparking a new wave could cause a bad impact... The protests will cause a delay in our economic recovery," Prayut said in a televised address.

Police said they will deploy 10,000 officers around the area to monitor the weekend's protest.

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