The nine Constitutional Court judges resolved unanimously to accept a petition initiated by 36 senators lodged against Ms Paetongtarn continuing as premier for consideration and temporarily suspended her from office by seven votes to two.
Deputy Prime Minister Suriya Jungrungreangkit has been confirmed as acting prime minister.
The kingdom’s politics have been dominated for years by a battle between the conservative, pro-military, pro-royalist elite and the Shinawatra clan, who they consider a threat to Thailand’s traditional social order.
The blow to 38-year-old Paetongtarn came on the same day that her father, former premier Thaksin Shinawatra faced a criminal court over allegations of royal defamation.
Paetongtarn took power less than a year ago but will be suspended while the Constitutional Court deliberates whether she breached ministerial ethics during the border row.
A long-standing territorial dispute with Cambodia boiled over into cross-border clashes in May, killing one Cambodian soldier.
When Paetongtarn called Cambodian ex-leader Hun Sen to discuss the tensions, she called him “uncle” and referred to a Thai military commander as her “opponent”, according to a leaked recording which caused widespread backlash.
Conservative lawmakers accused her of kowtowing to Cambodia and undermining the military, and allege she breached constitutional provisions requiring “evident integrity” and “ethical standards” among ministers.
“The Constitutional Court with a majority of 7-2 suspends the respondent from Prime Ministerial duty from 1 July until the Constitutional Court has made its ruling,” said a statement.
‘Critical dilution’
Paetongtarn’s Pheu Thai party has already been abandoned by a key conservative coalition partner over the scandal and thousands protested against her leadership in Bangkok over the weekend.
Thailand’s King approved Paetongtarn’s Cabinet reshuffle yesterday after her allies quit.
She assigned herself the culture minister position and is due to take up the position on Thursday, but it is unclear if she could take up that role while under investigation by the Constitutional Court.
Separately today, her father Thaksin arrived at a Bangkok criminal court to face accusations of breaching strict lese majeste laws used to shield Thailand’s king from criticism.
The allegations stem from a 2015 interview he gave to South Korean media and he faces up to 15 years in jail if convicted. The trial is set to last for weeks, with a verdict not expected for at least a month after that.
A court official confirmed to AFP the trial began this morning with Thaksin in attendance but said media would not be allowed in.
“I can’t speak on his behalf about how he feels, but I think he seems chill,” his lawyer Winyat Chatmontri told AFP outside court.
Thai political analyst Thitinan Pongsudhirak told AFP “there is a direct undeniable linkage between the two cases” as the brand of the Shinawatra family faces “a critical dilution”.
- Additional reporting by Bangkok Post