Untaxed airline baggage fees
To keep airfares down as fuel costs rise, airlines charge fees - some of which are federal-tax exempt - for reservation changes, seating, early boarding, meals, entertainment and baggage. Untaxed baggage fees in particular have generated $12.8 billion for airlines since 2007. If taxable, the revenue would help federally fund the air transportation system. Read related article.
Sources: Bureau of Transportation Statistics, U.S. Government Accountability Office. The Washington Post.