The social media company said it was "compelled" by the Thai government to prevent users in Thailand accessing Royalist Marketplace — a group with 1 million members featuring posts about the Thai royal family. Facebook said the government had deemed the content "to be illegal."
"Requests like this are severe, contravene international human rights law, and have a chilling effect on people's ability to express themselves," a Facebook spokesperson said in a statement to CNN Business. "We work to protect and defend the rights of all internet users and are preparing to legally challenge this request."
Thailand's Prime Minister Prayut Chan-o-cha on Tuesday defended the actions of the government in asking for the Royalist Marketplace to be blocked and threatening legal action.
"There is no such thing as special dictatorial power used in this case. The court's order has been properly obtained," Prayut said.
"Thailand has its own laws and everyone has to respect the laws of each country," he added.
Royalist Marketplace was started by Pavin Chachavalpongpun, an exiled Thai dissident based in Japan. Pavin did not immediately respond to a request for comment from CNN, but told Reuters that Facebook was "cooperating with the authoritarian regime to obstruct democracy and cultivating authoritarianism in Thailand."
— CNN's Kocha Olarn contributed to this article.