Prime Minister Prayut Chan-o-cha has called on National Reform Council (NRC) members to exercise their discretion when voting on the draft charter on Sunday.
His remark follows claims by both proponents and opponents of the draft within the NRC that their camp has gained the upper hand.
"You should be free to decide on your own," Gen Prayut said.
However, the premier cautioned NRC members, suggesting they be mindful of the consequences of their votes.
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If the draft charter is rejected by the NRC on Sunday, a new draft must be written by a new panel of drafters. If the draft is accepted but there is nothing in it to guard against renewed conflicts, there will be problems in the future, Gen Prayut said.
He made the comment as NRC members appear to be split over the draft.
NRC member Amorn Wanichwiwat said the vote was too close to call as several NRC members, particularly those who represent local administrations who previously supported the draft, are said to have had a change of heart. According to Mr Amorn, the no-vote is close to 130.
The proposed charter must receive a simple majority of yes-votes to be accepted. There are currently 247 members in the council. He dismissed estimates suggesting up to 200 council members will vote in favour of the draft constitution.
NRC member Boonlert Kachayutthadej said the draft charter was flawed and should be sunk. A good draft should receive an unanimous vote of support, but NRC members were split over the current version, he noted.
Mr Boonlert said the draft should be put on hold pending further revision. A new 21-member drafting committee should be set up to review the draft. He said it was the NRC which would be held to account if it passes the draft and new conflicts arise.
Fellow member Nimit Sitthitrai also said the NRC should vote down the draft if it doesn't measure up, rather than "passing the buck" to the people at a referendum.
If the draft is supported by the NRC on Sunday, a referendum is expected early next year. According to NRC member Sira Janejakha, about 190 to 200 members will vote for the draft charter.
The Pheu Thai Party, meanwhile, has stepped up calls for the NRC to reject the charter and spare the country from a new round of conflict, as well as avoid a waste of taxpayers' money in organising a referendum.
The party said yesterday that even if the draft is endorsed by the NRC, the public is likely to reject it at the referendum.
The party's remarks come two weeks after it published a "critique of the new charter" which attacked two provisional clauses: one calling for the appointment of 123 senators by a special cabinet-approved panel and the other calling for a "crisis committee" which can override the government in the event of a political impasse.
Among its supporters, People's Democratic Reform Foundation president Suthep Thaugsuban said on Tuesday the draft was "good enough" to give to the people for a vote.
Wattana Muangsuk, a core Pheu Thai member, wants early elections if the draft is voted down.
