Since Uber sets prices for a large portion of the market they operate in they have monopoly power and it's therefore not a free market. Uber's at 46% market share in major U.S. markets[0], since taxi's are regulated locally and Uber is setting prices for almost half the market nationally Uber is arguably the #1 regulatory power in the U.S. personal transportation sector.
[0] - http://www.forbes.com/sites/andrewbender/2015/04/10/ubers-as...