Thanatorn Losunthorn, the elected MP, must re-contest the election and win, if he wishes to occupy the seat.
Suthiphon Thaveechaikarn, Election Commission secretary-general, told a Bangkok press conference that Mr. Thanatorn, elected to parliament from Lampang's Constituency 1, was issued a yellow card after being accused of vote-buying.
Mr. Thanatorn allegedly violated election law by instructing his canvasser to hand out money to some eligible voters in the province, according to the EC secretary-general.
The EC's decision raises the number of PPP's winning candidates given yellow cards to four.
The poll agency previously issued yellow cards to three PPP poll winners in Nakhon Ratchasima for suspicion of poll fraud.
However, the four will be able to contest in the January 13 by-elections, unlike their three peers in Buri Ram province who were disqualified from the race after being given red cards for poll fraud.
The EC on Thursday certified 397 winning candidates in the December 23 general election, but suspended endorsement of 83 others, including 65 PPP elected MPs, pending further poll rigging investigations. (TNA)