The main opposition People's Party (PP) has submitted a bill seeking to amend the constitution to curb the National Anti-Corruption Commission's (NACC) authority to probe MPs and senators for ethical violations.
The PP confirmed it had presented the bill to House Speaker Wan Muhamad Noor Matha, according to Pakornwut Udompipatskul, a list MP of the PP in his capacity as opposition whip chief.
The submission precedes the ruling Pheu Thai Party's move to solicit support from coalition parties for its own bill to partially rewrite the charter, including sections governing political post-holder's ethics.
Political post-holders who violate standards of ethical conduct stipulated by the charter are liable for lifetime political bans.
A source familiar with the matter noted Pheu Thai's draft appears to be less precise than the PP's bill over ways to reduce the NACC's authority in judging ethical violation cases. These two drafts are expected to be deliberated alongside one another before being merged later when they reach the scrutiny stage.
On Tuesday, Mr Pakornwut said the PP-sponsored bill was being vetted before being slated on parliament's meeting agenda, a process that must be concluded in 15 days.
He expected the bill would be put to a debate at a joint sitting of parliament tentatively on Sept 25. However, the timing might clash with a debate on Pheu Thai's bill, in which case the PP would not mind rescheduling its draft for a later joint sitting debate.
Mr Pakornwut said the PP's bill stipulates amending the charter to systematically revise the grounds for ethical violations committed by political postholders.
Many in the House are concerned by what they perceive as a recent glut of spurious petitions designed to force them out of office over trivial or fictitious allegations.
The NACC is the agency receiving the cases before deciding whether to forward them to the Supreme Court or the Constitutional Court.
Mr Pakornwut said the amendment would need fine-tuning due to the charter's vague and "abstract" wording, which needs rectifying.
However, he echoed Pheu Thai's earlier statement that since the planned amendments concern the power of an independent agency, a referendum must be organised to endorse any changes made by parliament.
Meanwhile, PM's Office Minister Chusak Sirinil, who is also Pheu Thai's legal expert, said the party was looking to amend four to five sections relating to the ethical code for politicians.
He dismissed criticism that Pheu Thai's charter change plan was a self-serving move meant to emasculate the charter. The party simply wants ethical violations to be more clearly defined.