The constitutional amendment process is expected to be derailed as the ruling Palang Pracharath Party (PPRP) and senators will seek a charter court ruling on whether the process is constitutional.
A joint session of MPs and senators will today vote on a motion proposed by PPRP list-MP Paiboon Nititawan and Senator Somchai Sawaengkarn seeking the court's ruling.
In the motion, they said they were concerned that proposed amendments to Section 256 of the constitution, which will pave the way for the creation of a charter drafting assembly (CDA), may be unconstitutional.
The motion was signed by 47 senators and 25 MPs, all from the main coalition party, the PPRP, who claim parliament is not authorised to "make" a new charter and the most it can do is to make changes. Any action to allow the writing of a new charter would be unconstitutional, according to the motion.
Chaiwut Thanakhamanusorn, a PPRP list-MP, said that government whips agreed that each political party in the coalition government will be allowed a free vote on the matter, while PPRP MPs will vote for the motion.
A PPRP source said that key party figures were confident that the motion is expected to sail through parliament, given the support of 121 MPs from the PPRP and 250 senators -- more than half of 728 of the parliamentarians.
This would not necessarily need the support of MPs from other coalition parties, the source said, adding that senators wanted the court to rule on whether the CDA could write a new constitution.
Wirach Ratanasate, chief government whip and a PPRP list-MP, said that parties in the coalition government may have differing views so they will be allowed a free vote.
However, the support of PPRP MPs and senators alone would be more than enough to get the motion through parliament, Mr Wirach said.
He insisted that the move to seek the court's ruling was not an attempt to delay the charter amendment process, but it was only meant to seek a clarification from the court which has a final say on the issue.
Parliament adopted the two charter amendment bills -- one proposed by the government and the other by the opposition -- in the first reading on Nov 18 last year.
A parliamentary committee scrutinising charter amendments initially agreed to a proposal by opposition parties to set up a CDA comprising 200 assembly members who would be directly elected by voters from across the country.
Parliament will then convene for the second reading of the bills on Feb 24 and 25 when MPs and senators will hear the proposed changes, he said.
Unlike the opposition's envisaged CDA, the government's assembly would also comprise 200 members, but 150 would be directly elected and 20 would be picked by parliament.
Another 10 members would be law experts, 10 more would be political experts, and 10 would come from student groups.
Pheu Thai spokeswoman Arunee Kasayanont said that the motion seeking the court's ruling is a tactic to delay the charter amendment process which is against the will of the people.
"The coalition government's survival depends on the support of the Senate. Don't let the people lose trust. Don't add fuel to the flames," she said.
Chief opposition whip and Pheu Thai MP Sutin Klungsang said that the opposition parties will spell out reasons to oppose it during today's session.
"It is like walking into a killing zone which will shut the door on the prospects of charter changes, and a new constitution may not be ready for the next election," Mr Sutin said.
"The court may also rule that a national referendum will be required which will put the whole process back to square one," he said.
Jade Donavanik, a former adviser to the Constitution Drafting Committee, said that a court ruling on whether drafting a new charter would require a referendum would benefit the country as well as the opposition as it would provide clarity over the situation.
However, he warned against any efforts to delay the process so much that there would be no clarity on the structure of a new charter.
Ramate Rattanachaweng, spokesman for the Democrat Party which is the coalition parter, said the party has disagreed with the motion and all its MPs will vote against it at today's meeting.