U.S. Businesses cannot tweet using trademarked Olympics hashtags, but individuals can, according to the United States Olympic Committee. Olympic organisers may have been trying to protect sponsors and added certain hashtags to the list of trademarks.
Eric Goldman, a Professor of Law at Santa Clara University, thinks the USOC approach is overly aggressive and ridiculous. He told us "I think that trying to tell companies that they can't use the hashtag #Rio2016 or #TeamUSA in their tweets, most of the time they're going far afield of what the law permits and when companies use the ambiguities of trademark law to try and squelch socially beneficial conversation, I call that bullying." U.S. Business Cannot Tweet With Trademarked Olympics Hashtags [bbc.co.uk]