Defections from Pheu Thai by former MPs are a result of them feeling they are not receiving full backing, a party source has admitted.
The source, a former MP based in the Northeast, Tuesday said the former ruling party will continue to "bleed" former MPs.
"The floodgates have shown signs of breaking," the source said.
The comments come after the party was reported to be faced with the prospect of losing nearly half of its former MPs in the Northeast, its key stronghold, to a pro-regime party.
The defectors are thought to be joining the Pracharath Party which may support Prime Minister Prayut Chan-o-cha returning as prime minister after the general election slated for February.
Among the potential defectors are former MPs who represented Loei and former natural resources and environment minister Preecha Rengsomboonsuk.
Tuesday, the source said the defections are being caused by internal problems within Pheu Thai.
Many former MPs feel they are not receiving adequate support from the party which has not always been clear about its preparations for the next poll.
The source said the defections may only leave Pheu Thai with no more than 20% of its former northeastern MPs.
The party leadership is an unresolved issue.
It has been speculated key Pheu Thai figure Khunying Sudarat Keyuraphan has a strong chance of leading the party. However, she has not been named among its leaders.
The source added the party has failed to provide guidance for former MPs for months.
"If there is to be no clarity from the party, the former MPs feel they have the right to pack up and leave," the source said, adding: "Politicians need to find somewhere where they can feel secure."
Sanguan Pongmanee, former Pheu Thai MP for Lamphun, said if there is an effort by those in power to siphon off former MPs from political parties, this should be greeted as good news because it means they are serious about holding an election in the near future.