I read that as Niel was meddling in the gallo wars on the side of profaci which is against mob protocal because you're not supposed to go meddling in the affairs of other families unless the boss asks the other family's boss for help.
Profaci was the don. Neil was supposedly helping the don. Not sure how that could be against mob protocol.
Now, if Neil was sponsoring the insurgents, then I could see how that would ruffle feathers.