The main opposition Pheu Thai Party announced on Monday that it will file a motion in parliament on Tuesday to clear the way for a charter rewriting body to be formed, although it risks being vetoed by the Senate, according to a political source.
Pheu Thai's key figures told a press briefing on Monday that the charter amendment should be wrapped quickly and without a referendum after the changes are finalised.
The present charter was approved in a referendum on Aug 7, 2016.
Pheu Thai leader Sompong Amornvivat said the motion is centred on rectifying Section 256 of the charter to facilitate constitutional changes.
Under Section 256, a constitutional amendment requires the support of at least one-third of the Senate, or 84 senators. Critics have slammed the section as a major hurdle to fixing the charter.
Mr Sompong said the section should be altered so an assembly can be established to draft a new constitution, with or without the support of the Senate.
The Pheu Thai leader said other ways of pursuing the amendment would take too much time and that it would also be too costly to hold a referendum on the new charter.
His party encouraged the government and the senators to sign up for the motion.
Many lawmakers generally agreed that the charter was flawed and should be redrafted, although the methods of achieving the amendment vary.
Two pressing amendments which the opposition lawmakers are seeking concern the election system, which they have castigated as "complicated" and "unfair", and the appointment of the Senate, which is seen as favouring the government.
However, senators have said they will not back the proposed amendments if they would result in the Senate being stripped of its power to vote in a prime minister and/or the current batch of senators being dismissed.
"The issues which will be put up for debate must be clearly laid out first before the charter rewriting body can get down to work," said Senator Seri Suwannapanont.
"We won't give the charter rewriters a blank cheque to take the amendment matter into their own hands."
Mr Seri said that unless clear detail on the proposed charter's contents is provided, the Senate will not support the move.
He stressed that the current Senate was authorised by a provisional clause in the constitution to monitor the implementation of the country's reforms during its five-year tenure.
Pheu Thai Party secretary-general Anudith Nakornthap said that a House committee has been up and running for quite some time to study charter change.
He said the committee's members -- which include government and opposition members, as well as academics -- agree that the present charter's undemocratic nature is holding the country back.
Opposition chief whip Sutin Klungsang said that the charter panel must represent the people in deciding to adopt the changes proposed by a study panel headed by PM's adviser, Pirapan Salirathavibhaga, or reject it in favour of a different proposal.
Mr Sutin said amendments will be finished as fast as parliament can process it.
"We're looking at a likely timeframe of a year," he said.