I'm sorry, but working for minimum wage is not slavery. I do understand the point that the OP and others are trying to make, and I'll readily recognize an imbalanced class system, but there is a difference between actually being someone's property, having your family sold away from you, having no rights as a human being, and being poor. It is important to make this differentiation, in part because, as people on this board have been pointing out, human trafficking, slavery in the original sense, really does still exist in the world and to compare that to minimum wage work has the double danger of either implying that slavery is about as bad as working at a factory (something lots of people do and which most people have no problem allowing to happen) or that minimum wage work might as well just be slavery (if there's really no difference, why not just take that pay away?). I know this isn't where you were taking the argument, but it's where it could go.
Yes, there is a lot of injustice in the social classes. Historically speaking there have long been people at the lower end of the social ladder, people with very limited options, but who were none-the-less free citizens. This has always been regarded a distinct step up from enslavement. Pehaps it's true that now that we have more or less rid ourselves from accepting slavery as an institution, it is now time to start thinking about ridding ourselves of accepting this sort of minimal existence for impoverished workers, but I doubt on many levels that such a cause will be helped by calling this work slavery.