Pheu Thai Party core member Watana Muangsook reported to the 11th Army Circle on Monday after being summoned by the National Council for Peace and Order (NCPO) for his repeated comments against the draft constitution.
A number of soldiers were sent to Mr Watana's house on Srinakarin road on Thursday after he failed to contact the NCPO, but the politician was not home. He posted on Facebook that he would report to the NCPO at the 11th Army Circle on Monday, at 11am.
Shortly before 11am, Mr Watana arrived at the 11th Army Circle, accompanied by his wife and daughter. He stopped to talk with some other Pheu Thai core members including Chaturon Chaisaeng and Kittiratt Na Ranong at a military welfare shopping store for about five minutes. Also present at the store were representatives of the Swiss, Norwegian and Canadian embassies.
A group of soldiers walked up to Mr Watana, and took him away in a van into the military compound.
While being escorted to the van, Mr Watana told reporters that if by 3pm on Tuesday he was not released, it would mean he had been detained by the military by force.
He said he had sent a petition to United Nations secretary-general Ban Ki-moon. but had not sent petitions to other governments.
He also denied as untrue a report that he was seeking political asylum in Laos.
Lt Sunisa Lertpakawat, deputy Pheu Thai spokeswoman, said in addition to petitioning the UN Mr Watana sent a similar letter to 20 individuals and organisations throughout the world explaining about human rights violations in Thailand.
Narinpong Jinapak, Mr Watana's legal adviser, said on Monday if his client was not released by 3pm he would file a case against the NCPO for forced detention. He said it was a basic right of people to express their opinions on whether to accept or reject the draft charter.
He also commented that academics and core members of a main political party who had expressed similar views about the draft charter as Mr Watana had not been "invited" for talks. This showed discrimination on the part of the NCPO.
Mr Chaturon said the representatives of foreign embassies had voiced concerns about the human rights situation in Thailand and said they were surprised by the way Mr Watana had been treated by the military.
Mr Watana has been summoned for "attitude adjustment" four times for alleged violation of an NCPO order prohibiting actions which can be construed as detrimental to society, the economy and national security.