Mongkolkit Suksintharanon, leader of the Thai Civilized Party, on Monday filed a petition with the Constitutional Court seeking a ruling to settle Prime Minister Prayut Chan-o-cha's tenure wrangle.
The micro-opposition party lodged the petition ahead of a similar request to the court by all the other opposition parties tomorrow.
In his petition presented to the Constitutional Court office on Monday, Mr Mongkolkit asked for an injunction to suspend Gen Prayut as prime minister starting Aug 24 when some believe he will have served the maximum two four-year back-to-back terms, as stipulated by the constitution.
The injunction would prevent legal complications and damage arising from Gen Prayut working as prime minister beyond his term, he said.
Mr Mongkolkit said he submitted the petition as a Thai citizen and if Gen Prayut insists on remaining as prime minister after Aug 24, he will be looked upon as infringing on the people's right to have a new prime minister.
He said the case is admissible by the Constitutional Court. He urged Gen Prayut to bow out with dignity to defuse a political conflict stemming from his controversial time in office.
Cholnan Srikaew, leader of the main opposition Pheu Thai Party, on Monday confirmed the opposition bloc will submit a petition to the Constitutional Court over Gen Prayut's tenure via Parliament President Chuan Leekpai tomorrow.
The petition will also call for a court order suspending Gen Prayut pending a ruling.
Meanwhile, Deputy Prime Minister Wissanu Krea-ngam said the minutes of a meeting of the now-dissolved Constitution Drafting Committee (CDC) pertaining to a prime minister's tenure may carry some weight if they were admitted for consideration by the court.
The record of the CDC's 500th meeting is not likely to be a core document in the court's examination of Gen Prayut's tenure case.
During that meeting, charter drafters expressed their opinions about the tenure issue before the constitution was promulgated. The recording was not a resolution by the CDC.
The opposition indicated earlier that it would include the minutes of the Sept 7, 2018 meeting to support the view that Gen Prayut's maximum eight-year tenure ends late this month since he began serving as premier in August 2014, a few months after the National Council for Peace and Order he led ousted the Pheu Thai-led administration.
However, others contended that Gen Prayut's term ends in 2027 because he was appointed prime minister under the 2017 charter in June 2019.
But according to another view, the count started in April 2017 when the current charter was promulgated, meaning Gen Prayut's tenure ends in 2025.
Government spokesman, Thanakorn Wangboonkongchana, said the opposition has no business asking the court to suspend Gen Prayut over the issue.