The REAL ID Act was passed in 2005 and it requires certain security features to be on Drivers Licenses. The Department of Homeland Security announced a plan of enforcement two years ago. And in 2016, the agency will start enforcing parts of the act that require a driver's license meet federal standards in order for airline passengers to fly.
Certain states though, don't issue them as their regular Drivers License. So unless the states get a federal exemption, to take more time resolving the problem, people will have bring a second form of ID to fly.
Residents in New York, Louisiana, New Hampshire, Minnesota and the territory of American Samoa may need a second form of ID to Fly. Arizona already has an exemption.