Anybody making that comparison should go and study what slavery meant (and unfortunately still means) for a while.

I really find it unbelievable that someone would even contemplate such a comparison and think it a meaningful one.

Your employer does not own you, you can switch employers whenever you want - or you can stop working all together.

Nobody is going to come after you to murder you or haul you back if you run away.

No employer is going to sell you to any other, or take physical advantage of you.

You are not born into employment.

http://en.wikipedia.org/wiki/Wage_slavery

Is word play, it relates to being 'forced', but in reality nobody is really forced. It's just that if you want to take part in society you are expected to pull your weight, and that means either getting a job or doing your own thing (being self employed).