It Was Known I Was Joining Beforehand - Denied A Promotion Prior To Enlisting Into USAF Reserve?

I am employed with the Army & Air Force Exchange Service (AAFES). Almost two years ago I applied for a position in my department that was a Regular Full Time (RFT) position because the person vacating that position was made a supervisor. Regular Full Time is almost non-existent these days with AAFES (which I have been with since March 1994) because of them cutting corners anywhere they can. I submitted an application for the position and another employee who was much less knowledgeable on the products I sell applied, too. We were both in the same department. She got the job instead. Long story short.....8 months later she moved to a different AAFES facility and the RFT was closed out for good. Before this I had made it known among co-workers and friend s I was enlisting. In my interview for the position I was asked if I was still planning to join. I said yes. The interviewer (department manager at that time) says to me "I need to look out for the interest of the department and have bodies on the salesfloor and with you gone that would be difficult, have to hire temps while you're gone long periods of time, etc., etc.." So, I know that it is illegal for major companies to let you go for entering into the service or being deployed for so long, but is it legal to take into consideration that I was joining the service and deny me a promotion based on that? I am inclined to go to the base J.A.G. Office to inquire about this. I would like to know what you guys think about this issue?