Former Democrat election candidate Pongsin Senpong on Sunday announced his resignation from the party after failing to be selected to contest the general election under the party's banner.
Mr Pongsin, a Nakhon Si Thammarat-based politician and a younger brother of veteran Democrat Thepthai, said the party turned its back on him, so he decided to quit and other members of the Senpong family would do so as well.
He said the party's decision not to field him in the next general election showed a lack of appreciation for what the Senpong family had done for the party.
Mr Pongsin said he was a former candidate for the party while Mr Thepthai was a four-time MP for Nakhon Si Thammarat who fought against the Thaksin regime and faced 23 lawsuits.
"The Senpong family didn't abandon the party, but it was the party that abandoned us and didn't give us a chance," he wrote on Facebook.
Mr Pongsin stood and lost in the by-election in Nakhon Si Thammarat's Constituency 3 in March last year. Speculation was rife that Mr Pongsin would join the Ruam Thai Sang Chart Party (RTSCP) headed by former Democrat Pirapan Salirathavibhaga. He is the latest to quit after Trairong Suwannakhiri bade farewell to the Democrat Party last month after 38 years of membership.
Democrat leader Jurin Laksanawisit, however, insisted on Monday the party had not abandoned anyone, but it could only field one candidate per constituency. "It happens in every party, not just in the Democrats," he said.
He declined to comment on the mass defections hitting the party and expressed confidence the party would perform better than in the 2019 general election in which it picked up only 51 seats and none in Bangkok.
Elsewhere, the main opposition Pheu Thai Party will hold a special meeting on Nov 28 to prepare for the elections amid speculation the 23-member executive board would be revamped to avoid potential legal problems.
Deputy leader Sutin Klungsang downplayed the speculation, saying the planned meeting was to make sure that the party would go to the polls fully prepared.