Pheu Thai is beginning to count the numbers, asking all members to confirm their intention to stay with the party, or not, as it prepares for the long promised general election, with the polling date in February still uncertain.
Secretary-general Phumtham Wechayachai posted a Facebook message on Friday calling on all existing members to make their intentions clear to the party in the next month.
Former MPs and other members should inform the party's head office or representatives in electoral districts between Sunday and the end of April, he said.
Their membership would be completed after their details were checked by the party and registered. New members have to wait until political activities are allowed by the National Council for Peace and Order, he said.
The move is in line with the new organic law on political parties, which requires members to register with their party no later than April 30.
"All members who confirm their status and register with the party after April 30, 2018 will see their membership automatically void," Mr Phumchai wrote on the party website on Monday.
Former prime minister Thaksin Shinawatra said in Tokyo on Thursday he expected the party to sweep the election, but Deputy Prime Minister Prawit Wongsuwon has shrugged off the claim.
