Constitutional Court says Move Forward Party proposal to amend royal defamation law amounted to attempt to ‘overthrow the monarchy’.

The reformist Move Forward Party (MFP) finished first in last year’s election on a progressive platform that included a proposal to amend the lese majeste law that outraged Thailand’s conservative elite.

The Constitutional Court ruled on Wednesday the plan showed “an intent to separate the monarchy from the Thai nation, which is significantly dangerous to the security of the state”.

It also called it an attempt to “overthrow the democratic regime of government with the king as a head of state”.

The court’s ruling could set a precedent for any future review of the royal defamation law, which carries penalties of up to 15 years in jail.

At least 260 people have been prosecuted under it in recent years.

Earlier this month, jailed activist and lawyer Arnon Nampa was given an extended prison sentence for royal insults over a 2021 social media post.

In 2023, a man was jailed for two years for selling satirical calendars featuring rubber ducks that a court said defamed the king.

After winning the most seats and the largest share of the vote in May’s general elections, the MFP had its attempt to form a government toppled by lawmakers allied with and appointed by the royalist military. Then-leader Pita Limjaroenrat was blocked from becoming prime minister and the MFP was shut out of the governing coalition.

Some politicians have suggested there could now be legal efforts to seek the party’s dissolution and political bans for its leaders over its monarchy law stance.

Thanathorn Juangroongruangkit, the former leader of Future Forward Party – an MFP forerunner dissolved by court order – said earlier on Wednesday that the law should be up for discussion.

“The law is not a fax paper sent from God. It’s written by human hands, therefore people can amend it,” Thanathorn said. “If the lawmakers cannot amend the laws, I think something is wrong in the country.”

Thailand has been gripped in a two-decade battle for power between royalists, the military and old-money families against parties elected on populist or progressive platforms.