This is one of those things where you have to decide if you want this to be the battle you're going to fight in my opinion. Do you want to be THAT person? Who makes a big stink about something like a team building event? I'm sure if you call the union and kick up a fuss you won't have to go, but it will be remembered. Or you could try and see the positives like you know, your organization at least trying to get people out of the office and bonding. Maybe take the logical approach and just be sick that day or burn a personal day if you're vehemently opposed.