BANGKOK, June 27, 2025 (BSS/AFP) - Thailand's controversial ex-premier Thaksin Shinawatra goes on trial for lese-majeste next week with the kingdom teetering on the brink of political chaos, as his daughter faces being sacked as prime minister and activists threaten mass protests.

Southeast Asia's second-biggest economy looks set for a new round of the turmoil that has periodically gripped it over the last two decades as conservative forces renew their long-running tussle with the Shinawatra dynasty.

The coming weeks will see a series of court hearings that could terminate Prime Minister Paetongtarn Shinawatra's brief political career and send her 75-year-old billionaire father to jail.

Thaksin goes on trial from Tuesday accused of insulting the monarchy, which under Thailand's strict royal defamation laws could bring a maximum 15-year jail sentence.

The allegations stem from an interview he gave in 2015 to a South Korean newspaper, with the trial set to last three weeks.

A verdict is not expected for at least a month after that.

The lese-majeste laws shield King Maha Vajiralongkorn and his close family from insult or abuse, but critics say the laws are abused to stifle legitimate comment and debate.

The drama comes as the tourist-dependent kingdom seeks to reinvigorate its economy while heading off US President Donald Trump's damaging threatened trade tariffs.

Thailand is also grappling with a festering border row with Cambodia.

- Phone call crisis -

Paetongtarn's government hangs by a thread.

Its ruling coalition was slashed to a tiny majority by the departure last week of the conservative Bhumjaithai party in a row over a leaked phone call between the prime minister and former Cambodian leader Hun Sen.

In the audio of the call about the border dispute, Paetongtarn makes disparaging reference to a Thai army commander and addresses Hun Sen as "uncle".

Critics slammed the 38-year-old for insulting the military -- a powerful force in Thai politics -- and for being too deferential, calling for her to quit.

She apologised last week and managed to shore up her coalition, but now a group of conservative senators has submitted a petition to the Constitutional Court calling for her to be sacked.

The court may decide on Tuesday whether to accept the case, but its president, Nakharin Mektrairat, told reporters this week that it would be up to the nine judges to decide the timeframe.

If the court accepts the case, it may suspend her from office while it considers it, with a ruling expected to take several months.

- 25-year battle -

Paetongtarn's case and her father's trial are the latest round in a bitter 25-year arm wrestle between Thailand's traditional conservative, pro-military, pro-royalist elite and parties linked to Thaksin.

Thaksin was twice elected prime minister in the early 2000s and is still loved by many of the rural voters whose lives were changed by his policies.

But the establishment has long despised him as corrupt, nepotistic and a threat to the kingdom's long-established social order.

Thaksin was ousted in a coup in 2006, his sister Yingluck Shinawatra suffered the same fate in 2014 and other prime ministers from their political movement have been sacked by court rulings.

After 15 years abroad, Thaksin returned to Thailand in August 2023.

He was immediately ordered to serve an eight-year jail term for historic graft and abuse of power charges, but was taken to hospital on health grounds and later pardoned by the king.

That sequence of events has prompted a separate judicial probe into whether he got special treatment, and Thaksin's regular public appearances seem to have riled his old foes.

"His enemies never disappear -- they are still there, while new enemies have emerged and friends become enemies," Paradorn Pattanatabut, a former secretary general of the National Security Council, told AFP.

In a country which has seen a dozen coups since the end of absolute monarchy in 1932, the latest crisis has sparked speculation about another possible military intervention to oust Paetongtarn.

Tub-thumping posts on military-affiliated Facebook pages voicing vehement support for the army after Paetongtarn's leaked call have added fuel to the fire.

But a security source told AFP that a conventional tanks-in-the-street coup was both difficult and unnecessary, given the potential to stage a "silent coup" through the courts or other bodies such as the election commission.

Wanwichit Boonprong from Rangsit University agreed, saying this kind of "stealth authoritarianism" was more effective.

To add further spice to the mix, on Saturday a group of political activists involved in huge demonstrations that helped sink previous governments has pledged to hold a major rally calling for Paetongtarn to quit.