Can school authority enforce rules before and after schools done with?

Me and my girlfriend were walking down the hall holding hands and a teacher comes up and separates us and tells us it is PDA. Meaning Personal Display of Affection. They started this rule this year and so far I haven't had an issue with it. Thing is, it was Before school even started. So can they actually be the boss of me before it even begins? Same goes for the other day. When I was hugging my girlfriend good bye before I ran onto my bus a teacher tried to separate us. Like what the hell? I'm almost positive they can't do anything before or after school hours. What do you all think or know that can help me? And also its not like we were making out or anything. We were just simply hugging and or holding hands.