Germany's Interior Ministry said the HNG group is suspected of disseminating propaganda to neo-Nazis in prison to keep them from abandoning their beliefs and the movement, Deutsche Welle reported.
The raids in five states were organized by the ministry as part of an ongoing examination of the legality of HNG and similar right-wing organizations, the German TV broadcaster said.
The group's official objective is to support incarcerated neo-Nazi members and their families in an effort to "strengthen and overcome the ideological struggles in the fragmented neo-Nazi scene," ministry official Klaus-Dieter Fritsche said.
"We suspect that the actions of the HNG do not conform to our Constitution and that they threaten the cohesion of society," Fritsche said. "Today's searches will show if these suspicions are confirmed."
A 2001 German government report said the HNG was involved in of a number of non-constitutional activities, including the dissemination of Nazi propaganda and the use of Nazi and other far-right extremist symbols.