The Senate, as expected, voted overwhelmingly in support of the double majority rule to be applied in a charter amendment referendum on Tuesday.
In a vote of 153 to 24 with 13 abstentions, the Senate seconded the resolution of a joint House-Senate committee, which earlier stood by the double majority requirement.
The majority of senators voiced their disagreement with the House of Representatives, which insisted on forsaking the double majority rule in favour of a single majority.
Under the majority rule, more than 50% of voters must participate in the referendum, and the majority of those who cast their votes must approve it.
With a single majority, a winning vote of any size is deemed valid.
Many senators argued charter amendments are issues of national significance and a referendum must maintain a high standard in passing or rejecting them.
The MPs, on the other hand, warned that the bar being raised too high would risk hindering a charter rewrite.
A majority of senators stood their ground on the double majority rule even before the joint committee was established to iron out dissenting views between the two chambers. However, the Senate had its way in the committee, which voted to back the double majority rule.
On Tuesday, senators voiced concern voters may be persuaded to boycott the referendum in a deliberate act to force the turnout to fall short of the double majority rule.
Sen Nanthana Nathawaropas questioned whether there had been an "instruction" from some political quarters to back the double majority requirement.
She noted elections at all levels conform to single majority criteria. "Why then should a referendum be any different?" she said.
The senator belonging to the so-called 'New Breed" group said that a single majority was the democratic norm and any changes that create a double standard in democracy have no place in the country's rule.
Sen Pisit Apiwatthanapong, spokesman of the committee on Senate affairs and a member of the joint House-Senate committee, said the double majority rule applies only to the business of charter amendments.
He said he did not believe anyone would mount a campaign to dissuade voters from taking part in a referendum, as they would make themselves a target of criticism for being undemocratic.
Nikorn Chamnong, secretary of the joint committee, said it looks certain the majority of MPs will be unyielding in their support for the single majority requirement when they meet to discuss the issue on Wednesday.
If that is the case, the bill amending the referendum law will be put on the back burner for 180 days.
Later, if the House stands firm on its single majority rule, it will be adopted in the amended referendum law, paving the way for a referendum to be arranged.
After the referendum is given clearance from the Election Commission and the cabinet, the process of organising it would take 90-120 days.
"We're looking at a running course of 10 and a half months at least.
"The first [of three] referendums could be held in January 2026, to be followed by a motion in parliament seeking to amend Section 256 of the constitution," he said.
Section 256 pertains to the creation of a charter-drafting body necessary in the event of a wholesale charter rewrite.
Mr Nikorn doubted the process would be completed in time for the ordinary parliament meeting session, meaning it would be held up until parliament reconvenes in early July 2026.