Special interest groups: Groups with preferences that differ from the preferences of the median voter. There is nothing wrong with special interests forming groups per se; the trouble starts when they disproportionally sway policy in their favor.
“...the great enemy of democracy is monopoly, in all its forms: gigantic corporations, trade associations and other agencies for price control, trade-union… Effectively organized functional groups possess tremendous power for exploiting the community at large and even sabotaging the system.” Henry Calvert Simons - A Positive Program for Laissez Faire (1934)