The opposition is looking to petition the court and bring a no-confidence motion against Prime Minister Prayut Chan-o-cha for ethical violations stemming from his oath blunder, Wan Muhammad Nor Matha, leader of the Prachachat Party, said on Thursday.
The announcement follows the general debate in parliament on Wednesday, in which Gen Prayut was grilled for not having recited the complete oath of office during the cabinet's swearing-in before His Majesty the King in July.
Mr Wan Nor said the prime minister failed to explain the gaffe during the debate on Wednesday and there were grounds to take him to task for ethical violations.
Deputy Prime Minister Wissanu Krea-ngam, who is in charge of legal affairs, offered a clarification during the debate.
The fact Gen Prayut said nothing in his own defence and he did not deliver the oath in its entirety shows his intention to violate the constitution, which amounts to a gross ethical offence, Mr Wan Nor said.
The premier omitted the final sentence of Section 161 of the charter oath, which requires the oath-taker to uphold and abide by the constitution, during the July 16 oath-taking ceremony.
Mr Wan Nor said the seven opposition parties would meet to consider a petition to be forwarded to the Supreme Court via Parliament President Chuan Leekpai and the National Anti-Corruption Commission (NACC). They would decide on the content and how it should be worded.
The petition would be examined by Mr Chuan to see if it was supported by at least 151 MPs as legally required.
After that, Mr Chuan would pass the petition to the NACC, which would decide whether the alleged ethical violation holds water. If so, the agency would put the petition before the Supreme Court.
A source familiar with the matter said the court is authorised to set up an independent panel to study the prime minister's ethical conduct relating to the incomplete oath.
If and when the court admits the petition for consideration, Gen Prayut would be suspended from prime ministerial duty, and if the panel finds he has violated the code of ethics he would have to step down.
Mr Wan Nor added Gen Prayut would be subject to a censure motion over the oath issue in a no-confidence debate.
Mr Wissanu, however, did not foresee any problems with the opposition filing its petition. He cautioned that it must petition on the basis of the law governing the ethics of cabinet ministers, parliamentarians and members of independent agencies.
He said the Constitutional Court has said that taking the oath of office was strictly a matter between the government and His Majesty the King, and off-limits to scrutiny by "constitutional agencies" including the NACC.