The organizations are the Collegium Humanum, based in the city of Vlotho, and the Association for Rehabilitation of Persecuted Holocaust Challengers (VRBHV). The VRBHV is believed linked to the Collegium, which has been operating since the 1960s.
Interior Minister Wolfgang Schäuble described both groups as "collecting basins for organized Holocaust deniers."
Germany's domestic intelligence agency, the Office for Constitutional Protection, has had the Collegium under surveillance for some time. The association is believed to be a contact point for neo-Nazis and Holocaust deniers who dispute Nazi Germany's killing of more than six million Jews before and during World War II.