Pheu Thai party members have expressed disapproval towards the Constitution Drafting Committee's (CDC) move to entice people into voting for the draft charter first, with any amendments, if needed, to be undertaken later.
The disagreement came in response to comments made on Friday by CDC chairman Meechai Ruchupan, who said charter drafters cannot change the draft at this stage should it be deemed flawed, though it can be amended by those in power in the future.
Former prime minister and Pheu Thai key figure Somchai Wongsawat said Sunday Mr Meechai's comments reminded him of what he heard during the lead-up to the charter referendum in 2007.
After the 2007 draft passed the referendum, it could be amended only by a Democrat-led government, he said.
"As far as I can see, it is not easy to amend this draft charter," Mr Somchai said.
Responding to concerns about the public's understanding of the draft charter, Mr Somchai said people are anxious for it to be explained as it will help shape their decision to vote.
People should have the opportunity to learn about the draft as much as possible, he said.
The Pheu Thai party will make its position clear on the draft charter when it has the right opportunity, he said.
Pheu Thai's legal expert Chusak Sirinil backed Mr Somchai's concerns, saying it will not be easy to amend the charter once it passes the referendum.
Amending the charter requires support from opposition MPs and at least one third of senators, which will be appointed by the regime.
Failing to get these votes will make it impossible to amend the charter even if Pheu Thai wins as many as 90% of parliamentary seats, he said.
Acting Pheu Thai secretary-general Phumtham Wechayachai said the party has argued the referendum law deprives people of their rights to freely discuss and evaluate the charter, adding the law should be amended.
Former Pheu Thai MP Chaturon Chaisaeng said Mr Meechai's comment is an acknowledgement that the charter has flaws.
Many people also consider it is highly unlikely the charter will be amended if it passes the referendum, which can influence the way they vote, he said.
Meanwhile, most people agree reforms should be carried out before the election, according to Suan Dusit Poll's survey released Sunday.
According to the poll, 56.7% of 1,341 people surveyed across the country last week said reforms must be undertaken ahead of the election because the country has many problems that need to be addressed
In addition, 22.4% said the country's reforms and election should proceed side by side, while 20.8% said the vote must be held prior to reforms to expedite the election and mitigate the risk of political conflicts.