The People's Alliance for Democracy (PAD) will send its representatives Monday to petition the National Anti-Corruption Commission (NACC) to appeal the Supreme Court's acquittal of former prime minister Somchai Wongsawat and three others for abusing their authority in the deadly dispersal of protesters in 2008.
Former PAD coordinator Suriyasai Katasila said the group hoped the NACC, which serves as the plaintiff in the criminal case, will not shut the door on the people's opportunity to appeal.
"If the NACC does not appeal, I don't know how to explain to the people ... we hope the NACC will prove itself and gain the trust from the public," Mr Suriyasai said.
He added the National Council for Peace and Order may misunderstand and conclude the PAD is making a political move.
He insisted its move focuses only on how to plan on fighting the case involving the fatal crowd dispersal in 2008.
"There are no political implications whatsoever," Mr Suriyasai said, responding to Prime Minister Prayut Chan-o-cha warning the PAD against further political actions.
The case involves several parties and there are many victims of the incident.
The group needed to consult on how to proceed to ensure justice to all involved and to set a precedent for society, he said.
The PAD expressed dissatisfaction with a ruling on Wednesday by the Supreme Court's Criminal Division for Holders of Political Positions which cleared former prime minister Somchai Wongsawat and three others of abusing their authority in the deadly dispersal of PAD protesters in 2008.
The three others let off by the court were then deputy prime minister Chavalit Yongchaiyudh, 85, then national police chief Patcharawat Wongsuwon, 68, and then metropolitan police commander Suchart Mueankaew, 66.
Concerns have been raised about what the PAD will do if its demand is not met.
The NCPO still bans political gatherings that involve more than five people. The public assembly law also requires people wanting to stage a demonstration to notify authorities.