The four remaining occupiers at an Oregon wildlife refuge all face charges, according to court documents unsealed Thursday.
The indictment names a total of 16 defendants, including standoff leader Ammon Bundy and other occupiers who were arrested last week.
A federal grand jury charged all with felony conspiracy, accused of using intimidation to prevent federal officers from doing their work at Malheur National Wildlife Refuge.
The armed holdouts have said they wouldn't leave until receiving assurances they wouldn't be charged.
The indictment says two conspirators traveled to the area in October to warn the local sheriff of "extreme civil unrest" if certain demands weren't met.
Authorities arrested 11 people last week on a criminal complaint charging them with felony conspiracy. They were accused of using intimidation to prevent federal officers from doing their work at the refuge in sparsely populated southeast Oregon.