The taxi analogy isn't the same. The rates are being set by the local government, not some non-government third-party whom they work with like perhaps the people who actually own the medallions (most are loaned out) or the people who lease out usage of the vehicles, etc. If those places were setting rates on what could be charged then I'd say there's an argument to be made. Also, let's not forget why the government put in those rules on setting the rates in the first place - consumer protection. Cabbies were routinely ripping people off.

Furthermore, it's not just one thing. It's a set of criteria/tests that for certain states like CA and NJ are defined in the law. Taken in aggregate and not just on one single characteristic of the employment a determination can be made.