Effective January 1st, 2016, it will be illegal to sell bitcoin without a traditional money transmitters license. 

A money transmitters license is what corporations like Western Union, Ria, and MoneyGram are required by many state regulations to obtain for legal transfer of United States currency to and/or from individuals and legal entities residing in that state. Two famous examples of similar regulatory guidance or licensing requirements are those of Texas and New York.

In Texas the sale and purchase of Bitcoin is legal as documented in memorandum 1037 by the Texas Department of Banking. New York took a different approach and regulated the activity to the point of requiring those involved in digital currency transactions to obtain a virtual currency license (aka, a BitLicense) pursuant to 23 NYRCC 200, an overly expensive process that has been criticized for its fiscal compliance and lopsided approach in various excessive requirements in comparison to those of traditional licensing.