The new ballot system could open a window for a political party to win the next election by a landslide, Deputy Prime Minister Wissanu Krea-ngam said on Friday.
He was answering a reporter's question about a party's announcement that it intended to win an overwhelming majority in the next general election.
Mr Wissanu said the amendment to the charter to revert to the use of two ballots and change the composition of the House was intended to pave the way for such a result.
"When they proposed the change from one ballot to two and to change the number of constituency MPs [from 350] to 400 and list-MPs [from 150] to 100, they knew it could happen. They are veterans, so why wouldn't they see it?" he asked.
Talk of a landslide victory was sparked by Paetongtarn Shinawatra, the youngest daughter of fugitive ex-premier Thaksin Shinawatra, who last Sunday vowed to help the party win a huge victory and form a government.
Mr Wissanu said it would not be possible to go back to the one-ballot system unless the charter was revised.
The Pheu Thai Party was the only major political party that did not win a party-list seat in the 2019 general election, and the single-ballot system was blamed for that failure.
Meanwhile, Somkid Chuakong, a Pheu Thai MP for Ubon Ratchathani, said it was hard to predict how a vote on the candidacy number would turn out.
The parliamentary committee vetting the amended organic laws was scheduled to vote on March 30 if a political party should be designated the same number for both party-list and constituency candidates.
Mr Somkid said about 12 members were in favour while the rest were undecided, even though some appeared to see the merit in it.
He said the use of a universal candidacy number would be more convenient for voters and would help reduce the number of spoiled ballots.