Is it by law that each person that has a job MUST at least have 30 hours or more?

Okay so my mom works at chevron and she gets at least 30 hours a week. My moms friend got 7 hours a week.. One day he got so mad that he got 7 hours that he called 911 and left the station to the police... So is it BY law that you must have at least 30 hours or more?