Getting paid straight time instead of overtime in Michigan

My husband works for a armored truck company, and he is a driver. Right now they have him working 6 days a week, and getting about 65 hrs a week. They will pay him overtime up to 45 hrs. Anything over 45 hrs they pay him straight time. The supervisors on the other hand are getting paid the overtime. The reason given why the workers were not getting overtime is because they received "specialized training". My husband owns a chauffeur's licence, and already had a CPL training through the state of Michigan. There was no training for drivers beyond basic truck maintenance. Is getting paid overtime an option for employers? They don't have to pay it? My husband estimates he has probably lost about $2500 give or take in overtime pay. Is this legal for them to do this? What can he do??