The Italian-American Civil Rights League was a pain in the ass for the government, like Malcolm X and those guys.
The League also was a pain in the ass for Colombo soldiers. They had to waste valuable time shaking down store owners and others for League dues that they had to turn over to Joe without keeping any. Colombo's high profile put targets on their backs for law enforcement; and his denial that the Mafia existed diminished the fear factor that helped them earn.
There was never any evidence other than "leaked" reports to newspapers of Columbo soldiers shaking anyone down for the league.
