Senator Wanchai Sornsiri's negative remarks about Paetongtarn "Ung-Ing" Shinawatra of the Pheu Thai Party -- who is expected to be nominated as the party's prime ministerial candidate in the upcoming election -- have drawn criticism from his fellow senators, while the main opposition party has shrugged off his opinions.
The senator had said in a recent Facebook post that he won't vote for Ms Paetongtarn to be the next prime minister, even if Pheu Thai wins a landslide victory.
Pheu Thai leader Cholnan Srikaew on Monday said Mr Wanchai's comment is a violation of the rights and freedom of the people who support Pheu Thai and Ms Paetongtarn.
However, the party does respect the Senate as a whole and still believes the Senate will respect the voices of Pheu Thai voters, which would help the party win more than 250 seats in the House, he said.
Mr Wanchai's remark over the weekend simply was an opinion of an individual senator and should not be generalised as the opinion of all senators, he said.
Pheu Thai deputy leader Sutin Klungsang said he wasn't surprised by Mr Wanchai's comment, adding he is aware that the senator only supports either Prime Minister Prayut Chan-o-cha or Deputy Prime Minister Prawit Wongsuwon to return as the new prime minister.
Mr Sutin said he doesn't pay much attention to Mr Wanchai's opinion.
Some senators have moved to distance themselves from Mr Wanchai's comment on Facebook.
"What Mr Wanchai said in his Facebook post definitely was his personal opinion, not the opinion of the entire Senate or the majority of them," said Gen Lertrat Rattanawich, a senator.
The election of the new prime minister will be the last chance where all senators will be allowed to have a say in such an important selection; hence every senator will have to make a wise decision, said Gen Lertrat.
More importantly, the constitution stipulates that senators must maintain political neutrality, he said.
Personally, he said, he believes most senators will base their decisions on the number of MPs each party has won and the qualifications of each prime ministerial candidate.
The decision actually lies with all voters, he said.
Senator Kittisak Rattanavaraha also distanced himself from Mr Wanchai and his opinion, saying Mr Wanchai doesn't represent the Senate.
Mr Kittisak said he strongly believes most senators will use their remaining time in parliament in the best interests of the public.
"The person who these senators will trust to become Thailand's next prime minister must be someone who is knowledgeable, has a clean background, can ensure national stability and win approval at the international level," said Mr Kittisak.
That said, Mr Kittisak admitted that he personally thought Ms Paetongtarn was a little inexperienced for the high-profile job.
Senator Wanchai Sornsiri