The issue lays not with legality (it’s obviously illegal), but with a person’s (financial) ability to pursue legal recourse.
BUT, finances aside, people should always document everything. In person meeting or phone call? Follow up with an email recapping what was discussed. Make sure to take notes so you’re not relying solely on your memory.
Look for lawyers who would be willing to work on contingency. This is where they get paid when you get paid. If you have some money saved, you might be able to get away with retaining the lawyer.
Obviously a lot of people cannot afford a lawyer, and that’s a damn shame. Companies count on this fact and use it against their employees. But by documenting everything, you at least send a message to the company that you’re willing to fight back and that maybe enough in some cases to deter them (a long shot).
Also check with your state’s labor board to see what, if any, resources are available for workers in these type of cases.