The Bhumjaithai Party (BJT) will file a no-confidence motion against Prime Minister Paetongtarn Shinawatra amid the fallout of the leaked audio clip of her talking with Cambodian strongman Hun Sen.
Nan Boonthida Somchai, spokeswoman for the Bhumjaithai Party, said on Tuesday the party has resolved to submit a motion of no confidence against the prime minister under Section 151 of the constitution.
"The motion is set to be filed once the third parliamentary session opens on July 3," she said following a joint meeting between the party's executive committee and its MPs.
Ms Nan extended an invitation to fellow opposition parties -- namely the People's Party, Palang Pracharath, the Fair Party and Thai Sang Thai -- to co-sign the motion and support the no-confidence debate against the prime minister over her conduct.
Anutin Charnvirakul, Bhumjaithai leader, said at the joint meeting that the party has received strong support from local people, affirming that it has made the right decision to leave the coalition government.
"We will do our best as an opposition party, and none of our MPs have decided to leave the party after we joined the opposition," he said.
As the opposition party, the party does not support the Entertainment Complex Bill. Earlier, the party was on the government's side and had to support the bill, he said.
Meanwhile, Ms Paetongtarn said she is ready to respond to all questions posed by the Constitutional Court over the leaked audio clip, asserting that she has done nothing to damage the nation.
Ms Paetongtarn said that she is prepared to provide full information and clarification. She reiterated that the audio clip involved a type of diplomatic conversation commonly held between national leaders.
The content, she insisted, clearly shows that she had not caused any harm to Thailand.
She explained that the discussion was of a nature typically understood to be confidential and not intended for public release.
"The clip reflects a private conversation, and I am fully prepared to confirm and explain every aspect of the matter, should I be required to do so before the court," she said.
The leaked conversation included derogatory remarks about the commander of the 2nd Army Region, branding him an adversary, as well as a submissive tone towards Hun Sen, with Ms Paetongtarn signalling readiness to comply with his demands.
On Monday, sources reported that the National Anti-Corruption Commission (NACC) unanimously resolved to launch a preliminary investigation into Ms Paetongtarn over allegations of serious ethical violations related to her conversation with Hun Sen.
As part of the investigation, the NACC will transcribe and translate the foreign-language content of the audio, as it constitutes a key piece of evidence in the proceedings.
The source said the NACC emphasised the need to expedite the inquiry, given the significant public interest in the matter.
A coalition of political activist groups on Tuesday launched a joint campaign under the banner "United for the Nation" to defend Thai sovereignty and call for the resignation of Ms Paetongtarn.
The initiative includes prominent figures such as Jatuporn Prompan, a speaker for the People's Unity Group; Pichit Chaimongkol, leader of the Network of Students and People Reforming Thailand; and Panthep Puapongphan, Dean of the College of Oriental Medicine at Rangsit University.
Mr Pichit said that the United for the Nation movement will continue its campaign and has invited the public to join a major demonstration at Victory Monument on Saturday, calling on Ms Paetongtarn to resign.
People unable to attend are encouraged to show their solidarity by displaying the Thai national flag.
He also called on citizens across the country to participate in a coordinated singing of the national anthem at provincial halls or other locally designated venues in their respective provinces on Thursday.