The organ shortage continues to present problems around the world including the United States. In response, some countries have switched from an opt-in organ donor registry to an opt-out registry. The United States currently utilizes an opt-in registry where an individual is not considered an organ donor until they register their intentions. In the current study, U.S. adults were randomly assigned to a 2 (message valence: promotional, refutational) x 2 (autonomy restoration postscript: present, not present) x 2 (social proof: high likes, low likes) posttest only control group design evaluating social media message regarding an opt-out organ donor registry for implementation in the U.S. Results revealed an interaction between message valence and autonomy on freedom threat perceptions toward the message. Consistent with psychological reactance theory, freedom threat perceptions were positively associated with reactance, which in turn was positively associated with an intention to sign a petition and call a representative to voice disapproval of the opt-out organ donor registry. The discussion is focused on pragmatic recommendations for organ donor practitioners and advocates as well as the theoretical contributions to reactance theory.