Simple. At my place of employment, my labor is charged to a contract with a precision to 15 minutes. I'm obligate to perform 40 hours of chargeable labor across all contract assignment or I must fill the gap with PTO. If I work more than 40 hours (sometimes up to 70 hours), I don't get paid a penny more. What my employer does is divide my salaried cost for 40 hours labor by the hours I actually worked and shows the customer getting my services at a reduced labor rate per hour. Under very special circumstances, the customer might request extra labor hours to finish a critical item more rapidly. Those special circumstances are called Extended Work Week and hours beyond the standard 40 are compensated when recorded as EWW.
In a more common scenario, restaurants have promoted employees to "manager" and made their work salaried. They work well beyond 40 hours, but have a fixed income per week. Last time the Democrats meddled in this area, the companies converted the salaried managers to hourly employees and reduced shifts below the 40 hour threshold. Not a full time employee, so fewer or no benefits. No overtime. Additional part time employees covering the shifts. Major league blowback for the employees caused by Democrat meddling.
To the last question about whether salaried employees would be unionized...for my part...hell no. Thankfully, I'm approaching retirement. It will be nice to disengage from the long hours. 47 years of full time employment is enough.
I’ve been retired for some years now, so I am not up to date on the ever changing DOL exempt from overtime rules. That said, I think employers abuse the system. I moved from an hourly position to a salaried position at one point in my career. When I made the change, I was still declaring my time off in 15 minute increments. A few years later, the HR person said I only had to declare absences of 4 hours or more.