A story from a few years back I just remembered-
I'd taken one of my first jobs at a local grocery store chain. Within a month of working there, I'd noticed that the head cashiers had been calling me in a couple times a week, asking me to work unscheduled time because someone had called in. Half of my time spent working there ended up being non scheduled hours due to the frequency of call ins and not scheduling to accommodate for this.
So I took it to the store manager one day and explained the situation, and asked that if I'm going to be working all these hours with no notice, I'd like to be compensated for that. All I had in mind was something like the extra $1 an hour thing they did for when people worked Sundays. He looked at me with the most befuddled expression and responded with “… Your compensation.. is that you're being paid.”
Told him under no circumstances would I be covering for anyone in the future then and asked not to be contacted to work non scheduled hours. Who in their right mind thinks people want to be on call for minimum wage?