Senators have sent a strong signal that they may reject proposed charter amendments in the third and final reading on Friday, according to one member of the Upper House.
Senator Wanchai Sornsiri said on Monday that there is a feeling that the proposals serve the interests of some political parties more than the people.
They believed that the proposed changes would be a retrograde step rather than helping to steer the country forward, Sen Wanchai said, adding that the senators' stance should be clear one day ahead of the scheduled vote.
"I have kept my finger on the pulse of senators' opinions, and there are strong signals that they may not accept the charter amendment bill. We will have to wait and see as the situation changes daily," Sen Wanchai said.
Asked how more than 100 senators would explain such an apparent U-turn, Sen Wanchai said he was confident they would spell out their reasons.
"I believe the senators will make a decision based on the best interests of the public," he said.
He added that even if the amendments are passed, hurdles remain.
For example, those lawmakers critical of the bill are likely to petition the Constitutional Court to rule over its legality and the court will have 30 days to deliver a ruling.
If the bill clears the court, the next step will be for the prime minister to present it for royal endorsement which will take 30-60 days, he said.
On Aug 24, parliament approved charter amendments in a second reading to switch to using two ballots instead of one in a general election. Under the amendments, there would be one ballot for electing a constituency MP and another for a party-list MP.
The return of the two-ballot election system has been criticised for appearing to favour larger parties.