sin tax

(idiomatic, politics) A government-imposed tax on a specific good, service, or activity which is legal but widely considered to be unwholesome or socially harmful, such as a tax on alcoholic beverages, tobacco products, or gambling.

Example: 1963 May 1, Kathryn Baker, "White Facing Realities: Time, Cash," Victoria Advocate (Texas, USA), p. 16A (retrieved 29 Sep 2012):
  He has suggested raising “sin taxes” on cigarettes, liquor and arcade games to pay for the 24-percent teacher pay raise he supports.
1988 Dec. 19, Jan M. Rosen, "Tax Watch: The Likely Forms Of New Taxes," New York Times (retrieved 29 Sep 2012):
  Another form of consumption tax that some foresee is a “sin tax”, which would come in the form of higher excise taxes on alcohol and tobacco.
2009 April 2, Alex Altman, "A Brief History Of: Sin Taxes," Time:
  The sin tax is an established tactic. In the early 1500s, Pope Leo X underwrote his lavish lifestyle in part by taxing licensed prostitutes.