Can my employer fire me for going to MEPS?

On Monday I received multiple messages from my recruiter, telling me to come in immediately. I went directly from work (mcdonalds) to the recruiting station and was informed that they were taking my fingerprints. This process was an indication that they were going to send me to MEPS (Military Enrollment Processing Station) and told me they wanted to send me there Wed-Fri (because I was taking the language test). It was not an option for me to reschedule. Doing so would have caused me to lose the specific job I have been waiting patiently for. Directly after I had left the office I went to my Employers to inform them that I was going to be unavailable (Tues. but I'm not scheduled that day, so NBD) Wed. Thurs. and possibly Fri. I thought that a good notice face to face was more professional than calling in, especially since I wanted to hand him my recruiters’ phone number and some paperwork for proof since it was so short notice for the Both of us. He did not want to transcribe his number or look at these things. Regardless, I felt like it was a fair notice considering it was more than a full day beforehand. I asked to talk to the General Manager because he is in charge of both the employee and manager schedule. Not only was he there but another manager (M2) was, as well, who was manager on floor for Thurs. M2 checked the schedule and confirmed that it was fine and she would find a cover. General Manager told me I would need to find a cover for Wed. and inform M3 that I would not be able to attend my shift that day, yet when I asked for M3’s number General Manager said “I’m confused, I don’t understand why you would need M3's number.” After I explained my situation again he told he me he did not know M3's number. After some time he finally pulled a number for me to call and asked me to leave the store, didn't even give me time to look at the schedule, he kicked me out of the place because it was peak times. I seriously mean it when there were 0, seriously NO customers, it sounded like he just didn't want to deal with me. When I tried calling that number on Tues. it was a disconnected number. I had to be at the recruiters’ office for a pre-med. that day and I had already informed my employer that I do not have time to find my own cover.
On Wednesday I received a call from my Employer stating I was a no-call-no-show. I tried explaining to that I had talked to the GM about it on Monday and that I am at MEPS right now, so I could not come in that day. I made the conversation short because I was going through paper-work at that moment. They did not call me on Thursday. On Friday I called to confirm I would not be coming into work today. I was complained to that I had not showed up for my no-call-no-show Wednesday and Thursday shifts and I should talk to the GM, WHO I TALKED TO ON MONDAY. I asked M4if he wanted to transcribe my recruiters’ phone number so that he may ask him questions about it and he also told me he was not interested in receiving that information. I said OK and hung up. I went in 3 hours after I swore in, showed the GM my paper work stating what days I had been in MEPS. He said that I was not being responsible for my shift. I told him that he could not fire me because I was on duty for the Military (or that's my recruiter told me to tell them and another guy enrolling in the Army who also worked at a Mcdonalds didn't even tell his Employer that he was leaving for MEPS and got his job back!) and Serving my country is more important than serving burgers. Can this guy fire me?
I've had no problems with any job and the only problem I've had at this job was when I was yelled at for finding a cover for my own shift. (Unrelated to this time). Yet, now I'm being yelled at because I didn't find a cover for my shift, yet I gave them a Formal verbal and written statement (the written one they refused)? I told him that and when he was caught in the act he said "Yeah we really need to get our managers on the same page". GM said he'd call me later today and hasn't called me back. I'm crossed off the schedule too, I assume I've been fired without being told that I am fired! This confuses me. Anyway, I assume they are thinking about firing me, can they?

Sorry for any bad spelling.