It was one of two videos showing apparent arrests by undercover officers yesterday in Bangkok that sparked outrage on social media. The other shows two men pushing a woman at a peaceful protest into a moving taxi.
Police did not return several phone calls seeking comment.
Thailand's ruling military junta has launched a major campaign to suppress dissent since staging a coup on May 22.
On the sidelines of one of the protests, several plainclothes men escorted a woman to a motorcycle as she frantically called for help and asked them, "What right do you have to arrest me?" according to a video posted on the website of the Thai newspaper Matichon.
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One of the men is wearing a black badge around his neck that says "PRESS" along with a green cloth that looks like an arm band issued to reporters by the Thai Journalists Association and the Thai Broadcast Journalists Association.
He said the tactic would have an "immense impact" on both the safety and credibility of the media in Thailand.