The Pheu Thai Party has strongly criticised parts of the draft constitution, saying it "shows no respect" for people, and warned that it could stir up more political trouble, rather than end conflict.
"The constitution being drafted not only reflects a lack of trust, no confidence and no respect for people, and also strips away the sovereign rights of people," the party said in a statement issued on Monday.
The statement was written by the party's two key legal experts, Chusak Sirinil and Pongthep Thepkanchana.
The Pheu Thai position is in the same line as that taken by the Democrat Party. In an exclusive interview with the Bangkok Post, Democrat leader Abhisit Vejjajiva warned that the draft charter could lead to more conflict and snatch democracy from the people.
Pheu Thai substantiated its opposition to the draft charter by pointing to a proposal for the end of elected senators, who would be replaced by a selection process with a tenure of two consecutive terms.
Voters have no place in the selection of these "handpicked" senators, who could have excessive power, including the impeachment of a prime minister, that would damage the democratic principle, it added.
The party opposed another clause in the draft which opens the way for an outside prime minister. The charter writers claim that the option could help the country out in the event of a political crisis.
But Pheu Thai argued against the idea, saying: ''the draft constitution tries to set conditions for an outsider to be prime minister, which is moving (the country) backwards.''
This would ''clear the way for (people) to prolong their power and could bring about continued violent conflict'', it added.
The new government to be formed after the draft charter is promulgated would also be rocked by instability as it would give small- and medium-sized parties more bargaining power and weaken big parties, because the drafters favoured a coalition administration, it added.
Members of parliament would be given the freedom to not follow a party resolution, which could make it difficult for the winning party to make good on its promises to voters made during an election campaign, the statement said.
''What (the charter drafters) are undertaking is not a solution that will solve the country's problems, as everybody longs for,'' the party summed up in the statement.