Firebrand politician Watana Muangsook, of the Pheu Thai Party, has urged the regime to refrain from using its supreme power under Section 44 of the interim charter after a new constitution was signed Thursday.
King Maha Vajiralongkorn's signing of the new charter is a key prelude to holding a general election to restore democratic rule after the military government's 2014 coup.
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The former commerce minister said that once the new charter is enforced, the incumbent government will serve mostly as a caretaker entity.
"They [the regime] should know their status," said Mr Watana, adding its main role is supposed to be "preparatory work to be delivered to the new government".
Moreover, various parties have expressed concern about the freedom with which Section 44 can be invoked, Mr Watana said, describing this overarching power as a threat to democracy.
If the regime keeps resorting to this, the new government will not be able to function properly, he said.
"The undemocratic use of power must be eased or discontinued," he said, calling on the regime to use its "conscience" in such matters.
Mr Watana said his party is ready to contest the election.
He brushed aside concerns about the possible emergence of military-backed political parties.
More party choices are good for the public, he said, adding Pheu Thai wants to ensure there are no abuses of power in a bid to interfere with the election.
Meanwhile, Democrat Party leader Abhisit Vejjajiva expressed concern about an ongoing order banning political parties from holding certain activities.
Speaking at a ceremony marking the party's 71st anniversary, the former premier said he is waiting for a response from the National Council for Peace and Order (NCPO) on its fate, and believes the order will gradually be eased.
Until that time, the party will focus on preparing new personnel and policies, he said.
Referring to reports the Election Commission (EC) has begun dividing constituencies in preparation for the general election, Mr Abhisit said that even if the poll is held next year, the EC must not seek to redraw lines from the end of 2017.
Bhumjaithai Party leader Anutin Charnvirakul said he was confident Thailand would now return to democratic rule with the King as head of state.
His party now has 12 to 18 months to prepare for the upcoming polls in line with the regulations laid out under the new charter, he said.
Mr Anutin said his party will work on fine-tuning the details of four key policies that will be of the most benefit to the general public in the lead-up to the poll.
It is necessary for Bhumjaithai to field its candidates in all constituencies because all votes carry weight under the new charter, he added.
Referring to his relationship with the other political parties, he said Bhumjaithai is not in conflict with any of them.
The election results will dictate whether or not the party decides to join a coalition government, he added.
"We are ready to serve in any role," Mr Anutin said.
"If we become part of the government but can't get anything done then I would rather see us become an opposition party, as at least we could contribute more to the public in this role by providing the proper level of oversight," he added.
He dismissed rumours that Bhumjaithai has invited members of the National Reform Steering Assembly (NRSA) to join its ranks in the lead-up to the poll.
"No, it's not true. We are already happy with what we have now," he said.
