A bid to rid the Senate of the power to take part in electing a prime minister is underway in parliament as some lawmakers insisted such a change would uphold the Upper House's political neutrality.
A draft to amend the constitution to this effect was put before a two-day joint sitting that began on Tuesday.
A group of government and opposition MPs also called for a clause in the charter be fixed to require that a prime ministerial candidate can only be an MP. Currently, a non-MP can be nominated to take on the post.
Somchai Srisutthiyakorn, the Seri Ruam Thai Party's policy steering chairman who led a sign-up campaign to rid the Senate of its ability to pick a premier, proposed that a part of Section 272, which grants the Senate this power, be rejigged.
The rewrite would effectively mean the Senate can no longer jointly elect with MPs a prime minister from the names of candidates on the official list.
The constitution stipulates that the MPs alone would first have a go at electing a premier from the list of candidates nominated by political parties who won enough MP seats.
But if for any reason the MPs are unable to choose a prime minister from that list, some non-MP may be nominated for selection with the help of the Senate.
Many MPs are openly opposed to the 250 senators taking part in deciding who will lead the country, arguing they were hand-picked by the since-dissolved National Council for Peace and Order and therefore do not represent the public.
Mr Somchai said on Tuesday senators must always be politically impartial. But that principle stands to be compromised if and when they are compelled to make a political choice of who will serve as prime minister.
Their neutrality may be called into question, especially if the candidate they vote for is supported by any particular party, Mr Somchai added.
The former election commissioner said imbuing the Senate with this power would likely fuel social unrest.
He insisted the requirement -- whereby at least two-thirds of parliamentarians' votes are needed to elect a non-MP prime minister -- would remain intact.
Rangsiman Rome, a list MP for the Move Forward Party, said the Senate's right to co-elect a prime minister, if not removed, would allow Prime Minister Prayut Chan-o-cha to prolong his grip on power.
Meanwhile, the Internet Dialogue on Law Reform (iLaw), a Thai non-governmental organisation, said it has obtained information showing that as of Sept 30, 2020, at least 50 of the 1,830 members of senators' working groups were close relatives of senators.