Are 3 hour shifts legal in PA?

I work at GameStop as a ga and I'm getting fed up with the corporation treating their employee's like garbage. I recently began attending automotive school and gave my manager plenty of notice(MONTHS) since he was fired I've watched my hours decrease steadily- last paycheck I only got 6.75 after employee benefits were taken out(about $47 comes out of my paycheck and we get paid bi-weekly.) this is my only job, I work hard, and have essentially helped keep the store running since my boss was fired, despite being left without a manager or istant manager- we have a temporary stand in, and a manager in training but he's busy "running" his own store and she barely knows how to do the job of an SGA(one step up from my position). now hopefully you understand when I say that when I found out I was scheduled for two three hour shifts this week I was more than a little upset. I had heard that anything less than a four hour shift is illegal in the state of Pennsylvania- if that's true than I can talk to the overseeing manager or complain to HR- does anyone know? I'm surrounded by incompetent or inadequately knowledgeable employees, I can't afford groceries, I'm living off my brother's charity- and I'm about ready to quit- but I can't afford to.