Among those arrested were three terrorists defense lawyers—Arantza Zulueta, Jon Emparantza and Iker Sarriegi—a professor of fine arts, a member of the union LAB, and a former professional soccer player.
The detainees are accused of being envoys to ETA prisoners in order to maintain cohesion in the terrorist group.
"They were the political commissars of ETA [members] in prisons, and were in charge of establishing firm discipline among the group of prisoners," Rubalcaba said, according to EFE News Agency.
They are also charged with harboring terrorists, managing the payment of “revolutionary taxes, and recruiting gunmen.
The arrests are the result of a lengthy investigation carried out by the Civil Guard under orders from National Court Judge Fernando Grande-Marlaska.
During Thursday’s press conference, Rubalcaba explained that the investigations focused on the "illegal activities" carried out by the detainees for ETA prisoners that are not related to constitutionally protected attorney-client privilege.
Over the course of roughly 20 searches of the homes and workplaces of the suspects, various documents were seized containing information concerning future targets of the terrorist group.
The ETA is a Spanish terrorist organization that since its creation in 1968, has assassinated over 839 people and bombed several buildings causing the death of many innocent civilians.
