Non-governmental organisations have decried the 2nd Army's decision to summon 17 northeastern activists for opposing the military government's reform efforts.
The NGO Coordinating Committee (NGO-Cord) has denounced the interrogation of the activists, saying it undermines the military's own efforts to push national reforms.
The 17 were last week ordered to report to the 2nd Army after civil society groups issued a statement saying they would boycott reform efforts initiated by the National Council for Peace and Order (NCPO).
The statement said they will not cooperate with military-dominated bodies including the cabinet, the National Legislative Assembly and the National Reform Council because they disagree with the coup.
Soon after the statement was issued last Sunday, the 2nd Army either summoned activists by phone or sent soldiers and state officials to their homes before taking them for interrogation at military camps throughout the week, NGO sources said.
The individuals taken for interrogation include Suwit Kularbwong, secretary-general of the Isan NGO Coordinating Committee and a key figure in protests against potash mining in Udon Thani. Other activists and academics from Roi Et, Maha Sarakham, Khon Kaen and Si Sa Ket were also targeted.
The 17 were asked to sign papers consenting not to participate in political activities or criticise the military in public. The papers were similar to those given to people summoned to report to the military after the May 22 coup, the sources said.
The summonses have had a chilling effect on community and land rights activists as well as other human rights defenders, said Srisuwan Khuankachorn, chairman of NGO-Cord.
"These people are not political activists who stand up for fame. These people have been working closely with villagers whose land has been confiscated, crops destroyed, and houses relocated due to prolonged land rights conflicts," Mr Srisuwan said.
The 17 had been protesting against such problems long before the coup, but now are forced to keep quiet under martial law, he added.
Silencing NGO workers who are helping address the grievances of people will directly undermine the course of reform that the NCPO and government proclaims is its main agenda, he said.
"How will NRC members reach out to people who are facing real problems if they shoot down their ability to speak out," said Mr Srisuwan, who was a public supporter of the political campaign to oust the previous government.
The Thai Lawyers for Human Rights Centre said the NGO statement was an exercise in freedom of expression, guaranteed by Article 19 of the International Covenant on Civil and Political Rights.
The summonses impose a climate of fear and stifle such expression, the centre said, adding that martial law authorises the military to hold a person in custody for a period of no more than seven days and should be used only when there are reasonable legal grounds.
"It does not provide a blank cheque for military officials to act arbitrarily as they have done so far," the centre said.