Key personnel behind a failed attempt to pass a charter amendment bill providing for a "people's constitution" will continue their campaign to end the political monopoly.
Re-solution Group leader Parit Wacharasindhu on Wednesday admitted disappointment at the vote in Parliament that killed the bill sponsored by activists and members of the general public.
"The mission was not accomplished," he said in Parliament. "But attempts to amend the constitution will move onwards."
Re-solution joined the Progressive Movement, Move Forward Party and Internet Law Reform Dialogue in collecting 135,247 signatures on the petition calling for the amendment.
Mr Parit stressed the need to put an end to the Senate, saying the upper house was a mechanism to perpetuate the power of the elite.
The senators were handpicked by the coup-making regime, led by then army chief Gen Prayut Chan-o-cha. They played a key role in voting him into the prime minister's chair after the election.
The bill ended in its first reading after it failed to garner enough votes in a joint sitting. It needed 83 senators to vote for it -- but only three did.
Move Forward leader Pita Limjaroenrat said the vote "missed a golden opportunity" to move the country out of the political quagmire and promised to put the issue on the party platform in the next general election.
The country is divided between people who support Gen Prayut and those -- including street protesters -- who accuse him of using any means to cling onto power since the coup in 2014.
Progressive Movement secretary-general Piyabutr Saengkanokkul urged supporters of the bill not to give up and to continue the campaign to amend the constitution designed by the regime.