BANGKOK -- Thailand's pro-military government is spooked by the rumblings of discontent spreading among the country's youth. Young people make up the constituency that has rallied behind Thanathorn Juangroongruankit, the beleaguered leader of an anti-military political party.

Bangkok-based security sources say that the intelligence arm of the regime is tracking the messages spreading on social media for a public campaign against former junta leader and current Prime Minister Prayuth Chan-ocha. The event, "Run Against Dictatorship," was initially planned as a 6km run in Bangkok on Jan. 12. It has now spread to six more cities across the north, northeast and central regions of Thailand.

The organizers of the Bangkok event are an informal network of young, disgruntled political activists. They offer a measure of the event's rising popularity -- and rage against Prayuth. The initial registration had to be closed after 8,000 runners snapped up spots, according to the organizers' Facebook page. A second batch of registrations was opened to accommodate more runners. The event's Facebook page became an instant draw after it announced the event on Dec. 10, receiving more than 68,000 likes in the first two weeks.

The public display of discontent follows a wake-up call that Prayuth received on Dec. 14. Thanathorn had sent out a message the day before for a flash mob to protest injustice in a busy shopping district in the Thai capital. It drew over 5,000 pro-democracy demonstrators, becoming the largest protest against Prayuth since he led a coup in May 2014 as the army commander.

"The military, police and all were surprised by the number of protesters who turned out," a well-connected source within Thailand's security establishment told the Nikkei Asian Review. "They had asked around before the event and were expecting much fewer -- initially dismissing it as an attempt by Thanathorn to test the political waters."

Thanathorn Juangroongruangkit, leader of Thailand's anti-military Future Forward Party, talks to his supporters during a rally in Bangkok on Dec. 14.

People close to Prayuth are also taking stock of the unfolding mood on the ground among 20-something Thais and their political heroes in the Future Forward Party. "There are growing signs of disrespect for important symbols in Thailand, and we are taking note," one remarked, but was reluctant to elaborate. "This is not about forgetting, but about deliberate actions."

A survey of social media themes related to the FFP reveals how young Thais are railing against injustice becoming the law of the land and that they are not afraid to protest publicly. Some commented, "My body needs tear gas." There are also daring comments that touch on the Thai monarchy -- an extremely sensitive topic in the country.

Controversial court rulings and mounting legal cases against the photogenic billionaire Thanathorn and the FFP paved the way for Thanathorn's rise as a standard-bearer against injustice. The young voters who rallied behind the FFP enabled it to secure an impressive 80 seats in the March general elections. They are now openly referring to the "double standards" of the pro-establishment judiciary and the ultra-royalists filing court cases.

The view has been fueled by some cases in which the political allies of Prayuth's ruling coalition have received a slap on the wrist or no legal charges when they broke the law. One case grabbing the headlines centers around Pareena Kraikupt, a parliamentarian in the governing coalition, for owning a chicken farm that encroached on state land. Cabinet ministers have come to her defense than let her face the law.

Thanathorn already lost his parliamentary seat following one controversial ruling about failure to disclose shares in an obscure media organization. The FFP faces two more trials in January before the Constitutional Court, which could result in the party being dissolved.

Thanathorn supporters react as he arrives at a police station in Bangkok on April 6. © Reuters

Seasoned observers say one of the two cases could expose Thailand to international ridicule: the FFP is accused of being a member of the Illuminati, a fictitious secret society, which is viewed in ultraroyalist circles as a threat to the Thai monarchy.

Bangkok-based diplomats roll their eyes when talking about the case. But they are keeping tabs on the fate of Thanathorn and the FFP because "dissolving the FFP would be a setback to Thailand's transition to democracy," one diplomat remarked.

Thanathorn, speaking to a gathering of foreign journalists in Bangkok in early December, said, "After 262 days since we founded the party, we face 28 legal cases. ... We can see the attempt to stop us is real [because] the establishment doesn't want this transition to democracy to take place."

The sentiment has echoes in Thailand's recent political history. Thailand's ultraroyalist establishment succeeded in ousting two elected governments in the coups of 2006 and 2014, and turned to the Constitutional Court to deliver controversial verdicts to dissolve two popular political parties, disenfranchising large swathes of the country's poor who voted for them.

As Thanathorn readies for a likely showdown, he is getting help from some politically influential quarters to stand up to Prayuth and his political allies.

Among those backing him is Sulak Sivaraksa, 86, Thailand's foremost Buddhist scholar and champion of Gandhian values. "I gave him encouragement and said that one has to be patient when fighting dictators," Sulak told Nikkei in an interview in his Thai-style wooden home. "We have to be on the side of nonviolence and truth, which dictators don't have."