Facebook has blocked access in Thailand to a million-member group discussing the monarchy, after the Thai government threatened legal action.
The firm told the BBC it was preparing its own legal action to respond to the pressure from Bangkok.
Thailand is seeing a wave of anti-government protests which have included unprecedented calls for reforms to the monarchy.
Criticism of the monarchy is illegal in Thailand.
Access from within Thailand to the “Royalist Marketplace” group was blocked on Monday evening. The page can still be accessed from outside the country.
The group has more than one million members, “pointing to its massive popularity,” group admin Pavin Chachavalpongpun told the BBC.
Mr Chachavalpongpun said the group “provides a platform for serious discussion on the monarchy and it allows Thais to express their views freely about the monarchy, from the political intervention of the monarchy, to its intimate ties with the military in consolidating the king’s power”.
The self-exiled academic is based in Japan. A new Facebook group he set up on Monday evening gained more than 400,000 followers over night.
Facebook confirmed to the BBC it was “compelled to restrict access to content which the Thai government has deemed to be illegal”.
