Even living in an overly employee- focused labor law state like CA, I think there are some practices that should be avoided, if possible. However, retail in general is known for ever-changing schedules and changing hours. It is one reason I quickly learned, while in high school, that I didn't want to work retail.
Walmart, in particular, makes it almost impossible to hold another job. Schedules and days off change and you're expected to be there for your shift with a changing schedule, maybe a split day and changing hours.