Mr Nattawut Saikuar, secretary-general of the movement loyal to ousted premier Ms Yingluck Shinawatra, and Mr Pichai Naripthaphan, a former energy minister in her government, were both ordered to appear before themilitary after publicly criticising the regime.
So-called "attitude adjustment" sessions are used by the military to haul in those deemed to be uncooperative with Thailand's generals, who imposed martial law and took over in a coup last May.
At least five people - three former ministers, a Red Shirt leader and Yingluck's lawyer - have now been ordered to report this week.
Thailand's junta has moved swiftly to stamp out any renewed criticism of their rule following the retroactive impeachment of Ms Yingluck last week and after a top US diplomat made critical comments earlier in the week that infuriated the generals.
The military insist the summons are simply invites - though in reality any refusal to cooperate would likely lead to significant censure.
"Please use the word invite," General Udomdej Sritabutr, army chief and a key junta leader told reporters at Government House.
"We ask for their cooperation... and if they don't understand we will invite them again," he added.
Earlier this week junta chief Prayuth Chan-Ocha made it clear he would not tolerate those who spoke out against the regime, adding he would use punitive measures including banning critics from travelling abroad and having their assets investigated or seized.
During the same briefing Prime Minister Prayuth joked that reporters who continued to ask question that were not "constructive" might also be summoned.
The increase in "attitude adjustment" sessions comes amid a rocky patch for Thai-US relations following a recent visit by Mr Daniel Russel, the most senior US official to travel to the kingdom since the coup.
Mr Russel held meetings with junta officials and Ms Yingluck -- but not Prime Minister Prayuth - and delivered a speech warning that the military's pursuit of Thailand's first female premier risked being perceived as "politically driven."
Washington's top envoy in Bangkok pending the appointment of a new ambassador - Charge D'Affaires W. Patrick Murphy - was promptly summoned to the foreign ministry to explain M Russel's comments.
And Thailand's junta-stacked rubber stamp parliament on January 30 said they also wanted Mr Murphy to appear before them.
"We have verbally contacted the embassy and a written invitation will be sent soon," Ms Bilaipbhan Sampatisiri, chairwoman of NLA foreign relations committee, told AFP.
Thailand's generals say they were forced to seize power to end months of violent street protests against Ms Yingluck's government - part of a decade of political conflict that broadly pits Bangkok's middle class and royalist elites, backed by parts of the military, against rural and working-class voters loyal to Mr Thaksin Shinawatra.
Parties led by or aligned to the Shinawatras have won every election in Thailand since 2001.