Please give me some input as to whether my employer (a not-for-profit museum) is breaking any laws by underpaying a nonexempt co-worker for her work beyond 40 hours per week. She puts in a full 40-hour week as a receptionist, and often adds in at least 10 hours on the weekend for events coverage. For the ten+ hours, she is not being paid the time - and - a - half. She does receive a lesser rate.

Is there a law being broken?

Since she supervises volunteers, could she become exempt?

Not unless she's ALSO a volunteer, which it doesn't appear she is. Non-profits are not automatically exempt from the overtime provisions of the FLSA. The "non-profit" characterization is relevant for taxes only.

Is this a private employer or a government entity/quasi-governmental agency?

So your receptionist supervises the volunteers? Is she responsible for the overall volunteer program? Or does she just give general directions since she is presumably the first person they encounter?

Question #1 reply: The organization is a private nonprofit museum governed by a voluntary board of community members.

Question #2 Reply: The receptionist is supervised by the Assoc. Director, who technically oversee the docent program. However, the receptionist really does all the coordination, but not the training of docents.