The Democrat Party has called on the Constitution Drafting Committee to reject a proposal to allow the military-led government to maintain security during the transition to civilian rule.
The cabinet has proposed a temporary charter clause to keep peace and order after the general election and after a new government takes office.
Critics see it as a move by the military government to exert control over a new government and prolong its hold on power.
Democrat deputy leader Ong-art Klampaibul said Sunday that even though the proposal seems to be well-meaning, more detail is needed.
"The CDC should put it at the back of the drawer and ignore it. The scope of the proposal is still not clear," Mr Ong-art said.
If and when the draft charter is endorsed at the referendum, the democratic process should be allowed to take its course without the need for the military government, he said.
He said the draft charter puts in place enough measures to handle any future political crises, and empowers independent bodies and the Constitutional Court to help solve conflicts.
In light of this, there is no reason for the government to seek any special measure under the new charter, Mr Ong-art said.
With sweeping powers under the interim charter already at their disposal, the National Council for Peace and Order and the government should expedite efforts to address any urgent problems, he said.
"The proposal is none other than an attempt to stay on in power longer," Mr Ong-art said, adding the proposal could spell doom for the draft charter's fate in the referendum, expected in July.
Mr Ong-art also criticised the controversial national strategy bill which would set up a the national strategy committee to draw up a 20-year national development master plan for all elected governments to follow.
The bill proposed by the National Reform Steering Assembly (NRSA) is intended as a framework to carry out unfinished reform plans and ensure consistency in state policies on reform.
Mr Ong-art said the proposed national strategy would impose restrictions on elected politicians, saying political office-holders have the right to present their own policies to the public without having to worry what the strategy panel has in mind for the country.
Any development strategy also must gain recognition from all sides, Mr Ong-art said.
Nikorn Chamnong, Chartthaipattana Party adviser, joined critics of proposals for a military government to stay on after the election to maintain peace and order, saying the plan is undemocratic and could lead to conflict in itself.
Government spokesman Sansern Kaewkamnerd insisted the government did not want to cling to power, saying it is trying its best to carry out its promises to push for reforms.
Maj Gen Sansern said the government wanted the new charter to do all it can to prevent a repeat of past conflicts that occurred before the military coup on May 22, 2014.
CDC spokesman Amorn Wanichwiwatana said Sunday that the CDC had considered revisions to 60 clauses of the draft charter, based on feedback from stakeholders, while trying to maintain the main principles of the draft constitution.
Mr Amorn also said CDC chairman Meechai Ruchupan will meet Deputy Prime Minister Wissanu Krea-ngam to seek clarification over some charter proposals submitted by the government that are still "vague".
Observers said they include the proposal for a military government to maintain security after the election.
Mr Amorn said the government has said repeatedly it wants the draft charter to pass the referendum.
"So, we hope the government will not have any plan to derail the charter so it could stay on in power," he said.
