A dinner on May 23 between the opposition Pheu Thai Party and the Setthakij Thai Party and small parties is still on, according to Deputy Pheu Thai leader Yuttapong Charasathien.
He said there is no word from Capt Thamanat Prompow, secretary-general of Setthakij Thai Party, that he will skip the dinner.
It will be also attended Palang Pracharath Party (PPRP) MP Pichet Sathirachawal, New Economics Party leader Manoon Siwapiromrat and Chart Pattana Party list-MP Don Hetrakul.
He said if Capt Thamanat decides not to attend, he will file a petition seeking dissolution of the PPRP for dominating the affairs of another party under the law on political parties.
The threat follows reports which quoted PPRP leader Prawit Wongsuwon as saying Capt Thamanat would not attend the meeting with Pheu Thai.
The Pheu Thai Party warned that if Capt Thamanat did not show up, it could be a sign of PPRP interference in the Setthakij Thai Party.
Setthakij Thai is home to 18 MPs, including Capt Thamanat, previously expelled by the PPRP for acting as renegades. The group said it remains loyalty to Gen Prawit.
"We haven't received any word from Capt Thamanat that he will cancel the meeting. We only heard from Gen Prawit that Capt Thamanat won't attend. And if Capt Thamanat doesn't show up, I'll seek the PPRP's dissolution for dominating and interfering in Setthakij Thai's affairs," he said.
Mr Yuttapong said the May 23 meeting will focus on the controversial bidding for the main water transmission pipeline system for the Eastern Economic Corridor (EEC), which will be a key issue in the next censure debate.
The opposition plans to file a no-confidence motion against the government in the middle of next month, after the first reading of the budget bill for the 2023 fiscal year and the deliberation of the amendments to the two organic laws involving the election system.
Meanwhile, Mr Pichet on Wednesday threatened to sue for defamation four PPRP members who resolved to annul Mr Pichet’s rights to join the party's activities for six months.
The four were members of the PPRP committee on law and internal regulations, which found that Mr Pichet tried to subvert the party after he joined executives of the Pheu Thai in meetings on April 23 and May 4 to prepare for the no-confidence motion.
Mr Pichet said he would lodge the lawsuit because the committee's resolution had yet to be endorsed by the party but the four members went public with it and damaged his reputation.