BANGKOK — Another serious legal threat has hit the leader of Future Forward Party, this time an accusation of sedition.

Thanathorn Juangroongruangkit posted online on Wednesday a photo of a legal document showing that the Pathum Wan police have summoned him to hear charges over “causing disorder and disobedience among the public” that could lead to “the acts of rebellion.”

“When the dark power won’t leave Future Forward alone,” Thanathorn wrote in the accompanying post. “It’s clear now that the old-school political game won’t end after the election, but is only getting more intense, because they’re afraid of Future Forward.”

“They’re afraid of our wins that exceeded the expectations of many, afraid of politics based only on policies and ideologies that can build faith and support from the public without money or authority, afraid of the truth that nearly 6.3 million people sincerely support Future Forward Party,” he continued.

Thanathorn added that he would meet police investigators on Saturday as scheduled. If convicted, he faces a jail term of up to seven years.

The junta’s legal team said the charge was based on Thanathorn’s alleged involvement in a 2015 anti-coup demonstration, in which a group of activists staged a protest at the Pathum Wan police station. One of those activists was Rangsiman Rome, who might become one of Future Forward’s party-list MPs. The protesters were arrested and charged with violating the junta’s ban on political gatherings.

It’s the latest case of criminal prosecution and the most serious charge yet against Future Forward, a party with progressive policies that is popular among young people. The prosecutor’s office is also reviewing a cybercrime case against Thanathorn and two executive party members that involves online criticism of the ruling junta.

Thanathorn once served on the board of Matichon Group, which owns Khaosod English.

Party secretary-general Piyabutr Saengkanokkul said today that the police have also summoned him for reading a statement regarding the dissolution of Thai Raksa Chart Party and publishing it on the party’s website.

On Twitter, #savethanathorn shot to Thailand’s no.1 trending hashtag on Wednesday morning moments after Thanathorn posted about the sedition charge against him. Many users pledged their support and accused the military government of trying to destroy the party now that is has become a force to be reckoned with.

Although Future Forward started off as relatively unknown to the public and without any established politicians in its leadership, its unique stance opposing both the military and old-school Thai politics made it able to finish third at the polls, behind only political giants Pheu Thai and the junta-backed Phalang Pracharath.

The charge was revealed a day after army chief Gen. Apirat Kongsompong sent a warning to those who oppose the kingdom’s system of constitutional monarchy, which appeared aimed at Piyabutr who once advocated for reform to Thailand’s harsh lese-majeste law.