[Mr. Bird]

law enforcement officials used 311 technology to map out complaints by neighborhood and track down their source: illegal social clubs.

I'm not a NYer, so forgive my ignorance: what characteristic(s) would render a social club illegal? Are they referring to zoning violations (i.e. single family dwelling used as "clubhouse"), or is it more sinister, as it sounds?

[general_re]

Zoning, fire codes, liquor licenses - take your pick.

[vikk]

There are have been many of the sort all over the city, probably since the beginning. They usually fall into two catagories: illegal party spots for artists and hipsters in gentrifying neighborhoods, or ethnic illegal bars (usually Puerto Rican or Dominican) that don't want to deal with the usual paperwork.
They used to be winked at or allowed to exist as long as the right people got paid off until there was a horrific fire in a Puerto Rican one in the Bronx about ten or fifteen years ago. I think upwards of 115 people died, most by being trampled or suffocated by the crowd. All hell broke loose, and a lot of the illegal places got searched out and shut down by mayoral fiat.
Of course, they still exist, mainly because people forget and you can always grease a palm or two. Then there will be another tragedy, and we'll go through the same cycle again.