IIRC, the Nicolaitans were establishing a man-made institution which would direct believers in Jesus to follow strict behaviors and rely solely upon the ‘authoritarian’ dictates of the leadership, collecting monies like a ax system and dictating behaviors as if works were absolutely necessary to add to the Cross for ‘real salvation’. These ‘leaders’ went so far as to dictate who they would say were saved and who were not ... and with enough money in their pockets you could get their stamp of approved salvation.
Hmmm. Indulgences come to mind.