Context: Lets say your employer hires you and offers you payment at an hourly rate of $13/hr for time worked.
According to the department of labor's Klinghoffer rule, your employer can compel you to work without pay for as much time as needed so long as the time that you spent working without pay evens out to the federal minimum wage of $7.25/hr.
I find it odd that this is rarely discussed in the federal minimum wage debate, but all I can say is thats its extremely fucked up and depressing to know