Yes, in fact your employer can do this; such action is legally permissible. Absent a union/employment contract or company policy to the contrary, your employer is free to decrease your hours/pay/benefits at its discretion (as long as no minimum wage or like laws are violated). The fact is that in an "at will" work relationship, you employer can set the terms of your employment as it deems fit (absent engaging in workplace discrimination). For your part you can choose to work for this employer or not.