Earlier in January, a militia group led by Bundy seized the headquarters building of the refuge, which is operated by the US Department of the Interior, in protest over discriminatory US government land management policies and practices, which the activists claim contravene the US Constitution, as well as to highlight the jailing of two local ranchers for starting fires on federal land.
On Wednesday, the prosecutors said that at least 11 of the defendants had been charged with conspiracy to impede federal officers and intimidation. Their arrangement is scheduled for February 24.
Ammon Bundy is son of Cliven Bundy, an outspoken cattle rancher who confronted US Bureau of Land Management in the spring of 2014 over land grazing rights in the US state of Nevada.
The confrontation led to an armed standoff, in which heavily armed federal agents backed down. Many military veterans and members of self-described "patriot" groups came to Bundy's defense.