A fierce debate is expected in parliament on Tuesday as lawmakers will start discussing a charter amendment bill pushing for "a people's constitution".
The bill, which has the support of more than 135,000 eligible voters, proposes six key changes to the 2017 Constitution.
Lawmakers will vote on whether to accept the bill in the first reading on Wednesday.
The charter proposal seeks to abolish the Senate, which is seen as the proxy of the now-dissolved National Council for Peace and Order (NCPO). It also seeks to increase the MPs and the opposition's power to scrutinise government actions.
The bill also seeks to restructure the Constitutional Court, proposing that the court should comprise nine judges nominated by government and opposition MPs, and the general assembly of Supreme Court judges or Supreme Administrative Court judges.
The bill is sponsored by several groups including the Internet Law Reform Dialogue (iLaw), the Re-Solution group, the Progressive Movement and the Move Forward Party (MFP).
Senator Seree Suwanpanont said on Monday that the bill stands little chance of passing the first reading, due to the fact that it seeks to establish a unicameral parliament to replace the current bicameral parliamentary system.
Under the people's charter, the House of Representatives would serve as the sole legislative body, comprising 350 constituency MPs and 150 list MPs.
Mr Seree said this runs counter to the coalition government's charter amendment bill, which was endorsed by parliament in the third and final reading in September.
The coalition government's proposal sought to limit the number of constituency MPs at 400 and list MPs at 100.
"The people's charter is against the constitution and is unlikely to get through," Mr Seree said.
Senators will challenge the bill before the final vote, he said, adding that the bill requires the support of at least one-third of the Senate, or 84 senators, and at least 20% of opposition MPs, or 43, to pass.
Mr Seree also said the ruling Palang Pracharath Party (PPRP) will also reject the proposal because it contradicts the coalition government's bill, which is waiting for royal endorsement.
Mr Seree also brushed aside fears that anti-government demonstrations will become more violent if parliament rejects the bill.
He said that demonstrations will continue regardless of whether the bill is passed or rejected.
Newly appointed chief government whip, Nirote Sunthornlekha, who is a PPRP MP for Nakhon Sawan, denied speculation the PPRP will reject the bill.
Gen Prawit told party MPs to study the bill thoroughly before the debate, Mr Nirote said.
Cholnan Srikaew, leader of the main opposition Pheu Thai Party, said that parties in the opposition bloc will accept the people's charter in its first reading on Wednesday.
He insisted that their proposal is intended to end the coup-makers' hold on power and make the constitution more democratic.
Chaithawat Tulathon, secretary-general of the MFP, said that the bill will strengthen existing checks-and-balances and make those in power more accountable to the public.