sin tax

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A tax on certain items, such as cigarettes and alcohol, that are regarded as neither necessities nor luxuries.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun 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.