I don't know how easy it is to take to court in the US, but here it is beyond obvious what is an attempt at circumvention or not.

When I was in Uni I did a lot of contract work, when you register for being self employed they run you through a great set of questions so that you know whether you are self employed or not in the eyes of the law and what your rights are.

Of course most dodgy employers try to say 'you should register for self employment.. and I have to tell you to do so legally, but if you were to forget to do it you won't pay any tax and nobody will know, so don't forget to do it!' in the hopes that you don't bother yourself and don't end up finding out.