Does your civillian employer require to work around drill schedule when in the National Guard?

I recently got terminated from my job because my supervisor refuses to work around my drill schedule. I work at a Food Processing Plant and about this time we work weekends do we can get the food shipped to the store. When I told her that I was drill every month or going to be out for 3 days beginning in November, February (2015), and in June ( for annual training) plus I have appointment and visit a counselor every month as well and trying to go to school at the same time. I can tell that it wasn't sitting well with her and her supervisor. I also informed her that when I'm on orders it takes presence over everything and need to get to my designated place. My question is are there jobs out there that works around this whole ordeal going on? The reason I went to that particular food plant because the owner has a culinary class at Nichollas State so it wont be hard when I convert over to his school.
I'm trying to get in contact with the owner of the plant but he is never in his office. His secretary claimed that she emailed him the situation and I don't know if he is going to call me or what regarding the matter but I'm going to keep calling until he hear me out.