My question involves labor and employment law for the state of: Pennsylvania

In brief, I've been a good employee for 3 years of a large security company. I currently work 8:30am to 5:30pm at a site by myself. Back in October of 2012, i enrolled in classes starting in January 22, 2013. The classes begin at 5pm so, in October, i spoke with my manager about working at another site where i can work mornings, nights or weekends around my class schedule. He said that would be fine, we could work that out, and contact him again about it in December, closer to when classes start. Beginning of , I sent him an email, refreshing the conversation, and detailing my class schedule and availability to work any time around that. He did not respond to the email. I sent a text towards the end of December, no response. I called and left a Voicemail in January, no response, i called again a few days later and he picked up the phone, said "i will need to talk with you later" i replied "okay." We hung up, and i have not heard back from him. Today, i called him again, and left a Voicemail. I will be looking into escalating this above him today.

If this is not resolved by the time my classes start, and i leave my post early to go to class on time, what are my rights at that point? Can i be legally terminated? If i am terminated, would i be able to sue to get my job back? What are some options i have available to me?