The formation of a militia is included in the United States Constitution. In fact, it is often an element that is left out of the common gun debate, as the second amendment states the ability to bare arms in order to maintain a militia (not to simply store inside of a house), although the second aspect of the amendment is often overlooked by supporters.
However, with the ability to form a militia, many individuals have taken up arms in order to actually set up check points around the Bunch ranch, located in Nevada. Cliven Bundy made a few rather racist statements to the news in recent weeks, which has increased the desire to seek out the individual. However, this militia has taken its power further than allowed, and now they are harassing individuals who live inside of the city.
While it is possible to form a militia under the constitution, individuals still have their rights, which can not be restricted by others, including the militia. However, the militia is now illegally stopping all vehicles driving through and demanding the drivers show their license in order to prove they are actually residents of the town before being allowed to pass.
All of these individuals are heavily armed and are standing watch throughout the city, including near schools and churches. This is causing widespread panic throughout the city and is causing problems with workers needing to move in and out of the region for different tasks, or to simply drive through town.