A court in Thailand on Wednesday ordered the dissolution of the progressive Move Forward Party, which finished first in last year’s general election, saying it violated the constitution by proposing an amendment of a law against defaming the country’s royal family.

The Constitutional Court said it voted unanimously to dissolve the party because its campaign proposal to amend the law amounted to an attempt to overthrow the nation’s constitutional monarchy.

The Move Forward Party was unable to form a government after topping the polls because members of the Senate, at that time a conservative military-appointed body, refused to endorse its candidate for prime minister.

The Election Commission had filed a petition against the party after the Constitutional Court ruled in January that it must stop advocating changes to the law, known as Article 112, which protects the monarchy from criticism with penalties of up to 15 years in jail per offense. Move Forward has insisted that it wants to keep the monarchy above politics and not be exploited as a political tool.