More than a dozen leaders of Thailand's pro-democracy protest movement were charged Tuesday under the kingdom's tough royal defamation law for headlining demonstrations demanding reforms to the monarchy.

Thailand has strict lese majeste laws, enshrined in section 112 of the penal code, shielding the ultra-wealthy King Maha Vajiralongkorn from criticism.

But that has not stopped a youth-led movement from demanding reform -- including the abolition of the law in a direct challenge to the monarchy.

On Tuesday authorities summoned prominent protest figures to charge them under section 112 at police stations across Bangkok and neighbouring Nonthaburi province.

Eleven were charged for with lese majeste crimes the first time, but it was a second for three others -- Panupong "Mike" Jadnok, Parit "Penguin" Chiwarak, and Panusaya "Rung" Sithijirawattanakul.

Voicing defiance as they left the police station, those charged wore T-shirts emblazoned with the number "112" and a strike through it.

"The Thai government is using the monarchy and section 112 to target people who have different political stances," Panupong said, insisting the movement will continue unabated.

Thai anti-government protest leaders salute supporters before handing themselves in to the police at Nonthaburi police sation
Thai anti-government protest leaders salute supporters before handing themselves in to the police at Nonthaburi police sation AFP / Lillian SUWANRUMPHA

"Using 112 against us could light the fire for us, for the people who disagree with the existence of the law," he told reporters.

Anyone convicted under section 112 faces between three to 15 years in prison per charge.

The law has long drawn criticism from human rights activists, who say it is a tool to suppress dissent.

The use of it has slowed since 2018 due to the "mercy" of the king, according to Prime Minister Prayut Chan-O-Cha, but last month the premier gave the green light to deploy it again after months of protests.

Since then, some 16 protest leaders have been charged.

It will send the message that "the established centres of power... will ride out the storm and prevail at any cost", said political scientist Thitinan Pongsudhirak of Chulalongkorn University Tuesday.

But "tightening repression will likely radicalise the protest movement because their genuine grievances have no outlet", he added.

Besides calling for royal reform, protesters are demanding a rewrite of a military-scripted constitution and the resignation of Prayut -- who they consider illegitimate because as army chief he masterminded the 2014 coup.

Thailand