Senators want the Constitutional Court to decide if rewriting the charter and even the process of amending it should be allowed.
Sen Direkrit Jenkrongtham said on Sunday a group of senators had signed a petition asking for the court to consider three contentious proposals.
They are a change to Section 256, the setting-up of a charter drafting assembly and whether Parliament should also discuss a draft proposed by civic group iLaw, whose ideas are similar to the six other charter amendment bills already tabled for debate.
The charter change drafts are set to be considered by parliament next week.
The senators want the court to consider the legality of the proposal as Section 256 of the charter allows only a charter amendment, not a charter rewrite, said Mr Direkrit.
The required number of senators had signed the motion to be submitted to parliament, he said.
He also said he wanted to make it clear that the move was not aimed at delaying the charter change, just to make sure all things were done in accordance with the law.
Meanwhile, parliament can continue to debate charter change proposals.
Sen Kittisak Rattanawaraha said a group of senators, himself included, would ask the court to rule whether the six charter bills proposed by the government and the opposition were in breach of the constitution.
They would ask the court whether a referendum should be held before parliament could vote to whether to consider the bills in principle.
Government chief whip Wirach Ratanasate said the charter amendment had been scheduled to be discussed in parliament on Nov 17.
Pheu Thai MP for Bangkok Jirayu Huangsap on Sunday called on senators to promise they would not vote to select a PM before the process was over.
"Senators should find the solution that suits their positions by signing a confirmation that during the charter amendment process, if there is a vote to select the prime minister, they would all opt out from voting," he said.
"This is for the long-time grace and dignity of the senators."
