As in, you weren't scheduled but he asked you to come in? He can only take action against you if he asked you if you'd come in and you agreed to do so. That would constitute a schedule change, and therefore you were scheduled. If you never agreed to come in, then no.
Your employer can change your schedule to whatever he wants. But he must give you 24 hours advanced notice. If he did weather you agreed or not you must come it for your shift. And doing 12 hour shift is perfectly legal so long as you get 11.5 hours off between your shifts, and 2 full days off every 10.