When I started working in public sector I had to sign that I'm not a member of an unconstitutional group. As examples it included a list similar to this one: https://www.justiz.bayern.de/media/pdf/verzeichnis_extrorgan... It includes left-wing, right-wing, and islamist extremist groups.

Interestingly this list also contains the leftist party "Die Linke" which now has been a member of the federal parliament for a rather long time. That being said it's probably not a hindrance if you are a member there but you are expected to explain yourself.

Very interesting list, but perhaps it is meant to include some hardline former members of the SED?

Die Linke is seen by some as some sort of pariah in the German political landscape, due to its legacy and roots in the SED from which they never really distanced themselves in a very clear form. It's a bit of a touchy topic and the expansion to west Germany swept up a lot of nutcases, some of them in the more extremist spectrum. The topic gets even more confused since they're fairly well rooted in Eastern Germany where they are basically a left wing form of the SPD while they never managed to achieve that success in the West.

Interesting list indeed, and not only the entry for "Die Linke" is at least questionable