Oh they know, but they try to get around it. That's why unions are important - they keep their eye on this kind of stuff. Some companies try to get around the union by calling all of their salaried workers "managers" even thought their job descriptions do not align with the official definition. My husband worked for years for such a company, never got overtime unless there was a plant shutdown. He'd work way over 40 hours a week, and get nothing. He wasn't managing anyone, sat at a desk and reviewed systems, made plans for shutdowns. But there was no union for these "managers" so the company got away with it. He finally retired because of the stress and exhaustion he was dealing with daily.