"The rules should encourage the involvement of various professionals rather than become a ritual to sanction a pre-conceived charter dictated by coup makers," Suriyasai said in his capacity as secretary-general of the Campaign for Popular Democracy.

National Legislative Assembly (NLA) Speaker Meechai Ruchuphan issued the regulations on Wednesday, specifying that 2,000 National People's Assembly (NPA) members can cast one peer vote each to list three preferences for candidates.

Under the Interim Constitution, the 200 winning candidates will be ranked by number of votes received, and the Council for National Security is empowered to pick 100 to sit on the Constitution Drafting Assembly.

Suriyasai argued that Meechai should restrict each professional group in the NPA to vote among its peers instead of allowing all 2,000 members to vote across the groups.

He said the cross-group vote would benefit well-known personalities nominated by the coup leaders.

"I fear the voting outcome will favour senior government officials, military officers and leading figures at the expense of community leaders and those professionals from rural areas," he said.

Echoing Suriyasai, Democrat Party deputy leader Alongkorn Pollabutr said the regulations should be revised so that each professional group will be equally represented among the 200 candidates.

For example, if the NPA is divided into four professional groups, then each group should account for 25 per cent of candidates, he said.

Reacting to the criticism, Meechai said he was ready to amend the regulations although his critics should further explain how and why the amendments were deemed necessary.

"If the peer vote is done within a small group, then I suspect the outcome might be skewed because it is easier to sway votes from fewer voters," he said.

He said he saw no possibility to manipulate a block vote from 2,000 NPA members.

With regard to the large presence of university presidents and provincial governors in the NPA, he said the selection process was designed in accordance with demands from pro-democracy advocates.

"I am confused because many view academics and governors as respected figures and now you [critics] are saying you don't want them," he said.

He also said advocates from non-governmental organisations were allocated the NPA seats in accordance with their representation in the National Economic and Social Advisory Council.