If I give a two week notice to use my vacation time (which is company policy). Can my employer deny to give me that time off (after approving) and threaten to fire me if I take the time off that they approved, if there is mandatory training that I was not

I gave more than two weeks notice to use my vacation time and it was approved. The company I work for had some changes and forced the employees to change there schedules and we now have what they are calling mandatory training that we have to go to. In a very short notice mite I add. So now I am being told that if I miss the three days that I scheduled off a month ago out of a two week training I will lose my job. I need to know the legal answer to this please. I have worked for this company for over 4 years and have not missed any days without using my accumulated vacation time.