Was this at an imaginary McDonad's? McD's was my first job back in 96 at 16. They didn't have any unions then, and I've not seen or heard of any existing.
For the most part most fast food restaurants do not have any unions.
You want to look at a good example of a union look at the one for Autoworkers. My friend's dad growing up was in a good factory job, no college. He was earning >$22/hour, plus a pension, plus decent time off for vacations and things and the mom could be a stay-at-home mom.
Even on a programmer's salary, my wife and I still barely make our bills today. Rent's skyrocketed, cost of living has skyrocketed, and you need not look any further than the fact that nearly ever CEO (read: Billionaire) almost unamously has the goal to keep you, me, and everybody they know out of a Union.
Unions are not socialism. There is nothing bad about unions, some are better than others taken together all are better than none.