The Constitutional Court, a highly conservative institution, ruled unanimously against the Thai Raksa Chart Party, banning its executive board from political activity for 10 years.
The court blamed the party for endangering a tradition that kept the monarchy above politics.
The party, backed by self-exiled deposed prime minister Thaksin Shinawatra, nominated Princess Ubolratana Rajakanya Sirivadhana Barnavadi (pictured) as its candidate for the March 24 election.
Her brother, King Maha Vajiralongkorn, issued a royal order calling the nomination highly inappropriate and unconstitutional the day it was announced.
The party claimed that Ubolratana held no formal titles because she abandoned her royal role when she married an American man in 1972.
But she is still classed as a senior member of the royal family.
The nine-judge panel ruled that “even though she relinquished her title according to royal laws…she still retains her status and position as a member of the Chakri dynasty”.
Ubolratana posted on Instagram that the decision to dissolve the party was “sad and depressing”.
Party leader Preechapol Pongpanit said: “I and the party’s executives have the utmost regret over the party’s dissolution, which affects the fundamental political rights and freedom of the party members and the people.
“For me and the party executives, no matter what our status is, we will act for the benefit of the country.”
The election is being held under the new military-drafted constitution which makes it harder for Thaksin’s parties to win a parliamentary majority. The dissolution of Thai Raksa Chart is expected to further dent the Thaksin family’s chances of forming a government.
Rights groups denounced the verdict, saying it would diminish the fairness of the election that the generals say marks the return to democratic rule.
“This decision highlights the Thai authorities’ abuse of judicial powers to restrict the peaceful association and expression of the political opposition,” said Amnesty International’s Thailand campaigner, Katherine Gerson.
“This far-reaching measure raises strong concerns about the human rights to freedom of association and expression in the period leading to the election.”
Military-appointed Prime Minister Prayuth Chan-ocha is looking to retain the job after the election but he is not running for a parliamentary seat.
Under the divisive charter, a prime minister who is not a politician can be voted in by the upper and lower chambers.
The Constitutional Court has consistently ruled against Thaksin and his allies, whose parties have won every general election since 2001 but have twice been ousted in military coups, in 2006 and 2014.
Princess Ubolratana Rajakanya Sirivadhana Barnavadi. Picture credit: YouTube