The petition, signed by leading advocates such Weng Tojirakarn, Sant Hattheerat and Sunthorn Boonyod, was lodged with Decho Saowananont, deputy chairman of the Constitution Drafting Assembly.

The idea for condoning the seizure of power was incompatible with democratic rule, Weng said in reference to comments by National Legislative Assembly Speaker Meechai Ruchuphan and Constitution Drafting Committee chairman Prasong Soonsiri.

"The new constitution should not be reduced to serve one group of people or another, because it is the country's highest law," he said.

Meechai and Prasong both said it might be essential to include the amnesty clause in the draft charter, otherwise the country would be mired by legal battles relating to the coup.

At present, coup leaders are given immunity under the 2006 Interim Constitution, which will expire after the promulgation of the new charter.

In explaining his stand, Prasong said he circulated the idea of an amnesty in good faith in order to prevent trumped-up litigation designed to exact political revenge and inflame volatility.

Thai Rak Thai Party executive Adisorn Piengket said lawmakers could enact a law granting amnesty to the September 19 coup-makers.

"The amnesty can be granted under an act of Parliament. It is not appropriate to include such a clause in the new constitution," he said.