Well, The US is a corporation and gives out employment cards.
And, the cost of the employment card? All of the money you make and all the stuff you create is owned by The US.

The trouble is that... all of these documents say that when you reach the age of majority you can quit it.

However, since the world is so indoctrinated, and all lands have been split up to various corporations, you either are a corporate owned creature, or you have trouble living.