At least five members of the Democrat Party known as the "New Dems" have resigned after the party decided to form a coalition government with the Palang Pracharath Party (PPRP) on Tuesday.
The so-called "New Dems" who resigned are Parit "Itim" Wacharasindhu, Tanat Thanakitamnuay, Parit Ratanakul Serirengrit, Nattika Loweera, and Tadchon Klinchamni.
Mr Itim announced on his Facebook page that he decided to leave the party because the party's decision differs from his political beliefs.
"In order to allow the party to continue to be an uniting ground for people who share the same set of ideology, and to let it be driven by those who represent this set of ideology, I have decided to resign from my role as MP and party member," his post read.
Mr Itim, who was an MP candidate for Bangkok, said he had tried but failed to convince the Democrats to opt to become an independent opposition party.
Siripa Intavichein, the deputy spokeswoman of the Democrat Party, said about 30 members of New Dems are still with the party.
Ms Siripa, who is also the spokeswoman for the New Dems, said she is personally opposed to the party's decision to join the PPRP-led alliance. "But I choose to respect the party's resolution and continue working for the Democrats," she said.
The resignations drew various responses. "If you quit because you cannot bear the fact that the real world is different from what expected, that is just your ego talking," said economics lecturer Suvinai Pornavalai of Thammasat University.
Meanwhile, activist Nuttaa Mahattana praised Mr Itim. "Thank you for keeping your dignity and respecting people," she said on Facebook.