Opposition politicians are calling for parliament to debate their draft bill on a charter referendum before counter-proposals by the ruling party and its allies.
Parliament president Chuan Leekpai confirmed yesterday that opposition MPs were scheduled to formally present him with a motion seeking to amend the constitution today.
Pheu Thai, the main opposition party, is submitting its own charter amendment draft but two others are also being tabled for parliament's consideration, one sponsored by the ruling Palang Pracharath Party and another by the coalition Democrat, Bhumjaithai and Chartthaipattana parties.
It is understood Pheu Thai is pressing for its referendum draft bill to be heard first because it seeks to introduce sweeping changes to the charter and thus requires public approval via a referendum before they can be enacted.
Mr Chuan said Pheu Thai leader Sompong Amornvivat had told him the opposition would be submitting its charter amendment proposal today.
However, the joint debate on all of the amendment drafts by both Houses is not expected to begin until June 22.
Mr Prasert said members of the opposition parties met to discuss the amendment motion at the Pheu Thai head office yesterday.
The opposition bloc has reached an agreement on crucial issues, including how parliament must finish debating contents of the draft bill on the referendum before it proceeds to consider the draft amendment, he said.
The charter amendment motion being lodged today seeks to revise Section 256 of the constitution and pave the way for a charter drafting assembly, he said.
It also targets Section 272 of the constitution, which allows the Senate to join MPs in the selection of a premier and has been widely criticised as being a tool to keep Prime Minister Prayut Chan-o-cha in power.
Mr Prasert welcomed other opposition MPs supporting the proposed amendment to Section 272, which Pheu Thai is pursuing on its own.
Related amendments being sought include those on reverting the one-ballot election to a two-ballot system and abolishing charter provisions legalising all announcements and orders of the now-defunct National Council for Peace and Order.
Pita Limcharoenrat, leader of the opposition Move Forward Party (MFP), has accused the government of trying to prolong its grip on power and said his party refused to be a part of that.
The MFP would not take part in the PPRP's attempt to rewrite the constitution section by section, he said, and the draft bill on a referendum must be discussed first in parliament.
The party regarded the push to remove the Senate's ability to join MPs in selecting a prime minister to be of paramount importance, he said.
Prachachart Party leader Wan Muhamad Nor Matha said he opposed the government's attempt to have the amendment bill deliberated before the referendum draft law.