16.07.10 - From the U.S. Government and Accountability Office website:

Why GAO Did This Study
To supplement fare revenues, airlines are increasingly charging fees for optional passenger services, notably for checked baggage, for which separate charges did not previously exist. While air fares are subject to a 7.5 percent excise tax that funds the Airport and Airway Trust Fund, which helps fund the Federal Aviation Administration (FAA), many new optional fees are not.

As requested, this report addresses
(1) the nature, relationship to cost, and disclosure of airline fees,
(2) the potential impact of such fees on the Airport and Airway Trust Fund,
(3) checked and mishandled baggage issues; and
(4) the process, if any, for refunding government-imposed taxes and fees when passengers do not use nonrefundable tickets.
To perform this work, GAO analyzed financial data; reviewed applicable laws and regulations; and interviewed airline and government officials.

What GAO Recommends
If Congress wants to tax currently untaxed airline fees, it would need to amend the Internal Revenue Code. GAO recommends that DOT require airlines to consistently disclose optional fees and notify passengers of any refundable government fees; USDA determine whether its fee is refundable on unused nonrefundable tickets; and DHS issue guidance on the refundability of its fees. USDA and DHS agreed with the recommendations and DOT did not comment on them.

GAO Report (14 July 2010) Consumers Could Benefit from Better Information about Airline-Imposed Fees and Refundability of Government-Imposed Taxes and Fees

Thanks to Aviation Law Prof Blog