Most Democrat Party members agree with party leader Abhisit Vejjajiva's stance to reject the draft constitution in the referendum, says deputy leader Sathit Pitutecha.
The former Rayong MP said the party's 26 former MPs in the Central Plains provinces had come to a consensus to vote no in the referendum next Sunday.
"We stand united," he said.
Members were constantly assessing situations and looking at the party's direction in the evolving political context, he added.
Mr Sathit said the Democrats had a duty to explain the content of the draft charter, which some believe is weak in critical areas such as combating corruption and would give guilty politicians a second chance through appeals to the Supreme Court.
He said Mr Abhisit's stance on the draft charter announced last week was not intended to canvass for votes but to serve the public interest.
The party leader has come under fire from supporters for declaring he will vote no and for also rejecting the second question on the ballot as to whether senators should join MPs in selecting a prime minister.
Mr Abhisit outlined his reasons at a press conference on Wednesday. He argued that if the draft charter was passed at the referendum, it would undermine people's rights and freedoms while bureaucratic power would grow.
The significant role enjoyed by appointed senators could also provoke another round of political and social conflict, while the charter would also weaken the role and independence of anti-corruption agencies, he said.
Democrat Party spokesman Chavanond Intarakomalyasut said Mr Abhisit had made public his stance as leader of a political organisation responsible for imparting information about the draft charter, especially from a political perspective.
Mr Abhisit said if the draft charter was voted down in the referendum, he would support Prime Minister Prayut Chan-o-cha in drawing up a new draft that responds to people's needs and promotes national progress.
Mr Chavanond said Mr Abhisit's support for a new draft should not pile pressure on Gen Prayut.
If a new draft charter has to be drawn up and causes political groups to create unrest, the Democrats would resist any movement attempting to incite instability.
Mr Chavanond said the draft charter produced by the Constitution Drafting Committee led by Meechai Ruchupan should have offered more robust screening of people who will serve public office.
He said Mr Abhisit was concerned the draft charter was introducing an appeal system where those facing trial in the Supreme Court's Criminal Division for Political Office Holders may be able to find new ways to fight a case even after they have been ruled guilty.
Deputy Prime Minister Wissanu Krea-ngam earlier said the system complies with the United Nations convention that a person is entitled to an appeal in court.
Pheu Thai's former foreign minister Surapong Tovichakchaikul said yesterday he believed most people still do not understand the draft charter's contents.