BANGKOK - Mr Thanathorn Juangroongruangkit, the leader of the progressive, anti-military Future Forward Party, was disqualified as an elected Member of Parliament (MP) by the Constitutional Court on Wednesday (Nov 20), a decision that could potentially create a domino effect on his party's survival and the overall political status quo.

His disqualification is effective from May 23, the judges said. That was the day he was suspended as an MP after the Election Commission filed a case against him with the court.

Mr Thanathorn denounced the ruling as "giving more weight to assumptions rather than facts", and added that "the court did not mention my intent on violating Section 98 at all".

He was referring to Section 98(3) of the Constitution, which aims to prevent holders of political positions from influencing media through share ownership.

He insisted he would remain the party's leader: "The journey will go on. We will keep fighting."

The 40-year-old former auto parts tycoon was found guilty of violating the Constitution by holding shares worth 6.75 million baht (S$303,000) in a media company.

Maintaining his innocence and refuting the charge as politically motivated, Mr Thanathorn said he had sold his shares in V-Luck Media, a magazine publishing company, to his mother on Jan 8 and that the company had already ceased its operations before the electoral law came into effect on Jan 23.

But the judges deemed his defence to be "lacking weight" and "full of irregularities" as the share transfer was only reported to the Commerce Ministry on March 21. He had registered as an MP candidate in early February.

Over 100 supporters of Mr Thanathorn and his party turned up at the court, with some having travelled hundreds of kilometres from outside Bangkok to see him.

Holding a sign that said "#SaveThanathorn", Ms Pensri Janoo teared up after the ruling was delivered. The 47-year-old nurse, who took a day off to be at the court, said: "Mr Thanathorn is our hope. He's the one that can help move the country forward."

While the Future Forward Party holds strong appeal among the younger generation, 65-year-old Sunan Maneerat closed her handbag shop on Wednesday to show up in support of Mr Thanathorn.

"Thailand has no place for good people like him," she lamented.

Dr Yuttaporn Issarachai, a political science professor at Sukhothai Thammathirat University in Bangkok, told The Straits Times: "Thanathorn is the icon of Future Forward. Without him, their movement would be less influential."

Dr Yuttaporn says Mr Thanathorn's disqualification could have a ripple effect on his party's stability and very survival as the ruling can be used by the Election Commission to file a criminal case with the Supreme Court against him.

The politician faces jail time of up to 10 years if he is found guilty of running for office in knowing violation of election regulations. This sentence can, in turn, be used by the party's opponents to seek its dissolution and a political ban for its executives.

With Future Forward out of the way, the pro-military government coalition would gain a further advantage in Parliament, where it currently holds a razor-thin majority of 252 MPs in the 500-member Lower House.

Noting that the law extends members of a dissolved party a 60-day grace period to seek membership with another party, Dr Yuttaporn said, "It depends on the party's resilience and solidarity. If it can manage to form a new party and stay together, the party's influence in parliament wouldn't be diminished much.

"But even without their representation in Parliament, the party members can still continue their anti-NCPO activism. Their momentum won't be lost," he added, referring to the Future Forward Party's vocal opposition to military rule.

The National Council for Peace and Security junta held power from the time of its 2014 coup until the first half of this year.

Future Forward surprised many by winning 80 seats in the March general election - the first election since the 2014 coup - making it the third best performing party despite being founded only last year and the fact that none of its members had run for office before.

The controversial party and its key members have been slapped with multiple lawsuits during its campaign.

Mr Thanathorn himself has also been charged with sedition for allegedly aiding anti-junta protesters in 2015. A computer crime charge against him for criticising the regime on Facebook last year was dropped last month.

Regional lawmakers have expressed disappointment at Wednesday's ruling.

"Today's ruling is another indication that despite the holding of elections this year, Thai authorities are not ready for an open and free democracy," said Mr Charles Santiago, a Malaysian MP and chairman of the ASEAN Parliamentarians for Human Rights.