I've been reading all these comments from people who obviously aren't lawyers. They are self-certain and wrong. Yes, it is illegal to fire someone or reduce their hours based on health or medical issues (even chosen issues like pregnancy). And no, employment at will does not allow employers to do that, just as they could not fire someone because of the color of their skin.

Consult a real lawyer, not reddit people shooting off their mouths. From a lawyer who was general counsel of a company with many employees.