U.S. airlines generated US$3.4 billion from baggage fees alone in 2010, but that's just one piece of a growing pie of ancillary revenue raised by the industry in recent years to ease economic pressures. U.S. regulators are pushing to require carriers to report all of their ancillary revenue, breaking it down by category.

U.S. Dept. of Transportation issued a Notice of Proposed Rulemaking Friday that calls for requiring airlines "to report more information on the amount and types of fees collected from passengers, as well as the number of checked bags and mishandled wheelchairs," the department said in a statement. "The proposal would revise current reporting requirements to improve data collection on the amount airlines receive from different, specific types of fees."

Transportation Secretary Ray LaHood said the goal is to "make airline pricing more transparent ... In an era of rising fees, passengers deserve better information about how airlines are performing, particularly when it comes to fees, baggage and accommodating passengers in wheelchairs."

Airlines currently submit to DOT's Bureau of Transportation Statistics quarterly reports detailing revenue collected from baggage and reservation change fees. But money collected from ancillary revenue generators such as preferred seat assignments and onboard sales are not catalogued in airlines' reports to BTS.

DOT said the NPRM "proposes to require airlines to report 16 additional categories of fee revenue in addition to the baggage and reservation change fees." It additionally calls for changing baggage reporting requirements so that airlines, instead of reporting mishandled baggage in relation to the number of passengers enplaned, will report mishandlings based on the number of checked bags. DOT also wants airlines to report "more information about how well airlines meet the needs of passengers with mobility disabilities in order to understand and better address any problems."

The NPRM is open to public comments through Sep.13. U.S. airlines took a cautious stance toward the proposal.

"We are reviewing the proposed changes and will be responding," U.S. Air Transport Assn. said in an emailed statement. "As we have said consistently, we support transparency, and believe customers should always know what products and services they are paying for. We also believe the airline industry, vital to our economy as a creator of jobs and mover of people and goods, needs to be treated like other global businesses and free from unnecessary regulatory burden that add complexity and cost without delivering value."