Representatives from the United Front for Democracy against Dictatorship (UDD) and the now-defunct People's Democratic Reform Committee (PDRC) are expected to join in another round of public hearings on a draft "social contract for national unity-building" this week, according to the Internal Security Operations Command (Isoc).
Isoc spokesman Pirawat Saengthong said representatives of all groups had been invited to the event, hosted before the draft would be finalised.
In Bangkok, 400 participants from the Central region will include representatives from 70 political parties and NGOs as well as red shirts, supporters of the Pheu Thai Party, and the PDRC, who protested to oust the Pheu Thai government.
The forums for participants in different parts of the country will take place in military compounds from tomorrow until Thursday, starting in Bangkok (Central region), followed by Nakhon Ratchasima (Northeast), Phitsanulok (North) and Nakhon Si Thammarat (South) respectively, according to Col Pirawat.
Thida Thavornseth, a key red-shirt leader, said Jatuporn Promphan will represent the UDD. The group did not discuss its proposal for the forum this time as it had submitted proposals in previous rounds.
"The so-called social contract may be just bland proposals that should be acceptable for all, such as the people should seek reconciliation, adopt the principles of the sufficiency economy and avoid using hate speech. However, the point is the interpretation and the use of those principles in reality," she said.
She said it was possible that the social contract would be use to curb protests after critical political measures, considering that the ruling of the case against former premier Yingluck Shinawatra would come out soon.
Ms Yingluck has been charged with dereliction of duty for failing to stop corruption and irregularities stemming from her government's rice-pledging scheme.
The final hearing for defence witnesses is scheduled for July 21.
Mr Jatuporn said he would go alone and would see the content of the social contract draft first.
However, there would be no discussion of an amnesty or legal cases political players are facing.
PDRC foundation spokesman Akanat Promphan said on Saturday that he did not acknowledge the invitation and was uncertain who would represent the PDRC.
Prime Minister Prayut Chan-o-cha said these forums would gather more opinions from the public.
"I have ordered that in this social contract there must be practical guidelines, otherwise there would only be abstract proposals. It must be stated what must be cooperated such as respecting the law, no conflicts, no use of weapons -- these must be included in the social contract. If signed, there must not be chaos like in 2014," he said, referring to the political conflicts and violence before he seized power.
The process of drafting the unity agreement kicked off in mid-February when representatives from all sectors were invited to give their opinions on how to achieve national reconciliation.
The public's comments were gathered, categorised and drawn up into a three-page document, known as the social contract for national unity, by three panels set up under the committee for national reconciliation headed by Deputy Prime Minister Prawit Wongsuwon, who is also the defence minister.