The Pheu Thai Party on Wednesday fumed over proposals to allow provision for a non-MP to become prime minister in the new constitution.
Pheu Thai acting deputy secretary-general Chaowalit Witchayasut reiterated the party's strong objection to an outsider becoming prime minister and for non-elected senators.
Any attempts to allow a non-MP to be head a government and to bypass elections for the senate were contrary to democratic principles, he said.
Pheu Thai's renewed reaction followed an indication by Constitution Drafting Committee chairman Meechai Ruchupan that a charter to be written by the 21 members would include a provision for an outsider to become prime minister in certain circumstances. The outsider would be chosen by MPs, Mr Meechai added.
He also sent a signal that all senators will not necessarily come from elections.
Mr Chaowalit said this would be a move backwards.
The committee has about 180 days to write a new constitution.
The previous draft charter, dumped by the now-defunct National Reform Committee in September, also had a controversial clause opening the way for an outsider to be prime minister.
