(IANAL) California is an at-will state generally, so the answer is usually no. It is illegal in California for someone to be terminated for using their accrued

(IANAL) California is an at-will state generally, so the answer is usually no. It is illegal in California for someone to be terminated for using their accrued sick leave, and firing someone solely on their medical condition is also illegal. But these are folks who can't afford a prolonged employment discrimination lawsuit, and I've had patients lose their jobs for "other reasons," which an employer can easily come up with if they want someone gone.