The Bangkok Military Court on Friday accepted for hearing a case against 19 core red-shirt leaders for allegedly violating the regime's order which bans political gatherings of more than five people.
The 19 gathered during a press conference concerning the launch of anti-fraud centres in June.
The case was accepted after prosecutors agreed to indict the 19 key figures of the United Front for Democracy against Dictatorship (UDD).
The case was earlier forwarded to them by Crime Suppression Division investigators.
The defendants include UDD chairman Jatuporn Prompan, Nattawut Saikuar, Tida Tawornseth, Prasit Chaisrisa, Weng Tojirakarn, Nisit Sinthuphrai, Saranwut Sarankate and Yongyuth Tiyapairat.
The others are Korkaew Pikulthong, Veerakan Musikapong, Songkhram Kijpairote, Somwang Asarasi, Yotwarit Chuklom, Thanawut Wichaidit, Kirkmontri Rujsotthirapat, Aree Krainara, Somchai Jaimung, Sakrapee Phromchart and Pornsak Srilamut.
The court granted all the defendants except Mr Jatuporn bail on the condition that none of them leave the country, make political comments or stir unrest.
The move came after the 19 red-shirt leaders defied the ban when they gathered at a Bangkok shopping mall on June 5 to announce the launch of referendum-monitoring centres to ensure the charter poll on Aug 7 was fair.
Seventeen of the male defendants were detained and sent to the Bangkok Remand Prison. Mr Jatuporn is in jail for breach of bail conditions in a separate case, while Ms Tida was sent to the Central Women's Correctional Institution.
Winyat Chartmontri, a representative of the UDD legal team, said the prosecutors resolved to indict his clients as the act was deemed a political gathering in their view despite the fact that it was only an ordinary press conference.
Mr Winyat added they were willing to fight in court since the gathering cannot be regarded as a violation of the regime's banning because his clients had no intention of stirring up trouble and their gathering did not have a political agenda.
The UDD in June filed a petition with the UN Office of the High Commissioner for Human Rights (UNHCHR) in Bangkok.
It complained its rights were violated after it was banned from opening provincial centres to monitor possible fraud in the Aug 7 charter referendum.
At the time, Mr Jatuporn explained that the UDD decided to submit the petition to the UN because its centres were opened in only 47 provinces.
In 29 other provinces, UDD members were allegedly prevented from opening the monitoring centres by the regime.
Also, Mr Nattawut has said the political atmosphere during the lead-up to the referendum in Thailand was different to those in other parts of the world because the people had no rights or freedom.