About 30 members of the Thai Pakdee (Loyal Thai) group, led by ex-MP Warong Dechgitvigrom, on Tuesday submitted a letter to the Office of the Attorney General, asking it to seek the Constitutional Court's intervention to halt all moves to amend the 2017 constitution.
Mr Warong said efforts to amend the charter could be construed as intending to overthrow a democratic administration with the King as head of state.
He said the Thai Pakdee group was exercising rights under section 49 of the constitution to protect the country's democracy and the royal institution.
The group wanted the Office of the Attorney General to petition the Constitutional Court to put an end to the amendment process.
The 2017 constitution was the most beneficial for the people, according to Mr Warong.
As Thai Pakdee sought to curb constitutional amendment, parliament on Tuesday began a two-day meeting to consider seven charter amendment bills submitted separately by coalition government and opposition parties, and a civil group, Internet Law Reform Dialogue (iLaw).
"We believe some groups of people want to overthrow the royal institution by mean of drafting a new constitution," Mr Warong said.
"This is very dangerous for the country.
"Having submitting our letter to the Office of the Attorney General, we will await the result," he said.
The letter was accepted by public prosecutor Jitpatr Poomhiran, who said he would pass it on to the attorney general for consideration.