When a job has promised you a certain amount of hours a week and you took that job thinking that would be consistent but you get less hours, that should be considered wage theft. You most likely took that full time job because you were thinking it'd pay all your bills, or at least the majority of them. But when employers play with your paycheck by sending you home early because there wasn't enough to do or they scheduled too much staff for a day (which is a management issue), that is screwing with your livelihood because now you have to figure out what to do about those missed hours. They should at least pay you for the time you were supposed to be there if they send you home early.