this list is by no means intented to be conclusive, or correct, or even exact, and each one, if you would ask him, would probably give you a slightly different list.
these labels, especially at later times, also often made music in quite different genres.
the "big three":
Fischkopf (Hamburg)
Praxis (London)
Digital Hardcore Recordings (Berlin)
Deadly Systems (USA)
Killing Rate (Denmark)
Anticore (France)
Hangars Liquides (France)
Sans Pitie (France)
Epiteth (France)
Spite (Berlin)
CFET (Berlin)
Zero Tolerance (London)
Six Shooter (Belgium)
some of the output of PCP and sublabels can also be considered as being part of this style of music