The Collaborative International Dictionary of English v.0.48:

Whiskey Ring \Whiskey Ring\, or Whisky Ring \Whisky Ring\ . (U.
   S. Hist.)
   A conspiracy of distillers and government officials during
   the administration of President Grant to defraud the
   government of the excise taxes. The frauds were detected in
   1875 through the efforts of the Secretary of the Treasury B.
   H. Bristow, and most of the offenders were convicted.
   [Webster 1913 Suppl.]