Judgement day for Thailand's embattled Pita as parliament votes on PM

Thailand's prime ministerial hopeful Pita Limjaroenrat was braced for a critical test of his political clout on Thursday, as parliament convenes for a high-stakes vote on the premiership that could test the unity of his eight-party alliance.

The 42-year-old leader of surprise election winners Move Forward is expected to be the only candidate in Thursday's vote, but he faces a big challenge in securing the required backing of more than half of 750-member bicameral parliament.

The liberal Move Forward and its alliance partner, Pheu Thai, thrashed conservative pro-military parties in the May 14 election, seen widely as a resounding rejection of nearly a decade of government led or backed by the royalist military.

But Pita's determination to pursue Move Forward's progressive, anti-establishment agenda puts him at odds with a powerful nexus of conservatives and old money families that have loomed large over Thai politics for decades, and will be almost certain to try to thwart him in Thursday's vote.

Pita has had a bumpy ride and was dealt a major blow on the eve of the vote when two legal complaints against him gained momentum, prompting hundreds of pro-democracy demonstrators to gather in Bangkok to warn of moves afoot to keep Move Forward from power.

The Constitutional Court agreed on Wednesday to take on a complaint against the party over its plan to amend a strict law that prohibits insulting the monarchy, just hours after the election commission recommended the court disqualifies Pita as a lawmaker over a shareholding violation.

"There have been attempts to block, not to block me but block the majority government of the people from getting to run the country in various ways," Pita told ThaiRath TV.

"This is quite normal for the path to power in our country... All the big and important things are always difficult. I am encouraged and hopeful to fix things as they come until the dream of mine and the people can be reached."

The cases against Move Forward are the latest twist in a two-decade struggle for power in Thailand fraught with coups, court interventions and crippling street protests.

More turbulence can be expected if Pita fails to prevail in the vote. His alliance controls 312 seats, but to get the required 376 votes, he is banking on support from some of the 250 members of an upper house Senate appointed by the military in the wake of a 2014 coup.

If Pita fails, the alliance must decide whether to back him again in another vote, slated for next week, or put forward another candidate, testing its cohesion as it seeks to form the next government.