Several Future Forward Party (FFP) MPs claim they have been offered 30-120 million baht each to vote for Gen Prayut Chan-o-cha as prime minister.
Party spokeswoman Pannika Wanich and 13 other Future Forward MPs - some of the many who reported approaches -- held a briefing on Tuesday to disclose attempts to turn FFP MPs, almost all of whom are first-timers, into "cobras".
In Thai political terms, a cobra is an MP of one party who defects to another for money or other incentives.
She said the methods ranged from offers of cash and positions to direct and indirect threats.
Ms Pannika claimed the attempts had been financed by large business groups who supported the military coup.
Pathum Thani MP Anawin Rattanastaporn said he was approached twice. The first time he was offered 30 million baht — 25 million upfront and 5 million after the PM vote. "I turned it down. They later doubled the bid, but again, I said no," he said.
Bangkok MP Taopiphob Limjittrakorn, who champions beer production liberalisation, said he was first offered 30 million baht through acquaintances.
"They did not give up and upped the bid to 50 million, 70 million and, last week, 120 million. I turned them all down and told them no price can be put on democracy in this country. People's trust definitely is worth more than 120 million," he said.
Khon Kaen MP Thitinan Sangnak said he was invited to meet a puyai [senior figure] at the deputy party leader level but turned the offer down. The latest bid was 5 million baht upfront, 75 million after the vote and a 200,000-baht monthly salary, he said.
Ms Pannika said by now it was clear Palang Pracharath was now attempting to form a government from 150 votes. Since they could not survive going forward with these votes, they have to buy them from MPs of other parties.
"The success of an MP, regardless of which party he's with, comes from working to protect people's interests and forming a government to solve people's chronic problems, not by cobbling together 20 MPs for 400-500 million. FFW is confident our MPs are bound by ideology and there's no 'cobra' in the party."
She also confirmed the anti-military alliance of seven parties, including FFP, would propose FFP leader Thanathorn Juangroongruangkit as prime minister. "A PM candidate should share their vision in Parliament for everyone to see."
Although the Constitutional Court suspended Mr Thanathorn from performing his MP duties, Parliament President Chuan Leekpai has the final say on the matter and he said earlier a PM candidate could explain his vision of the future.
The PM vote is set to begin at 11pm on Wednesday. Unlike the speakers' vote earlier which used a secret ballot, it will be a roll call.