Amazon could say screw it and make all the warehouse employees salary exempt.
No, they can't. There are strict rules about who can be made exempt. Factors such as being allowed discretion in executing your work, flexibility in setting your schedule, being allowed to take time off without being docked, whether or not you have any "management" responsibility ... all play into it.
I once worked at a place for about six months. The job was supposed to be salaried (exempt), not hourly, and I knew that going in. But I also had a signed letter of offer from the company stating that, in general, I was being hired to work 40 hours per week. The nature of the work was somewhat crunch--slack--crunch--slack, so I expected and could put up with a couple of late nights once in awhile. But -- I had to attend in-service classes to maintain a license/certification, and they started docking me for the time I spent attending mandatory classes. And, even though I (and everyone!) was supposedly "exempt," they paid me (and us) for overtime -- but at straight time, not time-and-a-half.
After another personnel/human resources stunt they pulled, I quit -- and since work was scarce at the time and they had recruited me from a solid job I otherwise would have still been in, I felt no qualms about applying for unemployment. They contested it, we went to a hearing, and the hearing officer ruled that their various departures from the terms of their letter and from the terms of their personnel manual constituted "constructive discharge" (in other words, they forced me to quit) and that I would receive compensation. Further, he sent me on to the wages and hours group, who determined that since I was being docked for time off I was not being treated as a salaried employee but as hourly, and therefore they owed me time-and-a-half for all the overtime I had worked at straight time.
Employers can't just say "You're exempt" to everyone on the staff.
