Tropicans hold protest very rarely and become rebels or guerrillas instead. I've seen only one natural protest during my thirty hour like play. However you can anger environmentalists and their escalation is the mass protest. I don't know whether it's intended or not but most of the time those protesters doesn't appear and protest ends as soon as it began. However if you're lucky they'll appear at each mining, power plant and industry buildings. You can deal with them by clicking the megaphone icon. So trigger environmentalist escalation with actual protest few times and bribe all of them.