In 2000, Takara took action against an unauthorised comic book that was to be sold at BotCon Japan. The author of the book was ordered not to sell the book and instead give it away to attendees for free. There has never been another BotCon in Japan ever since.
http://www.botcon.com/archive/2000j/index.html
http://tfwiki.net/wiki/BotCon_Japan_2000