More than 30 MPs, including some from the ruling Palang Pracharath Party (PPRP), are expected to defect to the Bhumjaithai Party ahead of the next general election, according to a source.
This could help the party meet its goal of winning 120 seats in the polls, expected next year, the source said.
The potential defectors, from both government and opposition parties, signalled their intention to join Bhumjaithai while attending the 64th birthday bash on Tuesday of Newin Chidchob, a prominent party figure who some believe to be its de facto leader, the source added.
Some of the 30 MPs who are allegedly willing to jump ship were spotted attending a ritual associated with birthday celebrations known as Pakam Chang, which was organised by the Chidchob family.
The party, which attracted many well-wishers and politicians, took place in Buri Ram on Tuesday.
MPs who may be looking to switch sides, according to the source, include: Thanat Thawi-kueakunkit, a New Economics Party MP for Tak; Anucha Noiwong, a PPRP MP for Phitsanulok; Nop Chiwanan, a Pheu Thai MP for Ayutthaya; Bunthida Somchai, a Democrat Party MP for Ubon Ratchathani; and Natthaphon Charatraphiphong, a Thai Economic Party MP for Surin.
Other possible defectors met Mr Newin and wished him a happy birthday in private but were not seen at the family rite, the source added.
Among them were Monthian Songpracha, a PPRP MP for Chai Nat; Pathomphong Sunchan, a PPRP MP for Nakhon Pathom; Prathuan Sutthi-amnuaydet, a PPRP MP for Lop Buri; and Krit Kaeo-yu, a PPRP MP for Phetchaburi.
Others included Nanthana Songpracha, a People Progressive Party list-MP; and Samak Pongwong, a Chartpattana Party MP for Samut Sakhon.
Deputy Prime Minister and Public Health Minister Anutin Charnvirakul, in his capacity as Bhumjaithai leader, led party members of the cabinet who attended the celebration.
Mr Anutin dismissed media reports about his party wooing MPs from other parties, saying Bhumjaithai's door is open to anyone who is talented and determined to work in politics.
In the case of Mr Nop from Pheu Thai, Mr Anutin said he had never approached the MP to join the party, regardless of media reports to the contrary.
However, Surasak Phancharoenworakun, a Bhumjaithai MP for Ayutthaya, said Mr Nop plans to move to Bhumjaithai when parliament's term ends in March.
Mr Nop, who has been open about his intention to defect and was at Mr Newin's party, declined to speak to reporters.
Mr Newin also stayed tight-lipped about any defections. He only told well-wishers that Bhumjaithai is targeting at least 120 seats in the next election.
Mr Anutin joked later that Mr Newin's wishes always come true.