Sen. Charles Schumer (D-N.Y.) is urging the U.S. Transportation Department (DOT) to require airlines to disclose fees for carry-on bags alongside fare quotes in customer searches—a proposal, conceivably, that the department could take up as part of a passenger rights notice of proposed rulemaking (NPRM) it is slated to unveil in August.

The prominent Democrat sent the letter to Transportation Secretary Ray LaHood on April 4 after Allegiant Air unveiled its new fee ranging from $10 to $35 for carry-on bags. But Schumer did not go as far as he did when Spirit unveiled its plans for a carry-on bag fee in 2010; at that time, Schumer introduced a bill that would make carry-on fees subject to the 7.5% federal excise tax that currently is limited to fares.

In going to the DOT, which has been more willing under LaHood to push what it calls “passenger protection” regulations, Schumer could find more fertile ground than in Congress. But Schumer’s proposal is not too far removed from an idea that the DOT considered—and rejected—in its passenger rights rulemaking last year.

At that time, the DOT considered its own proposal to compel airlines to produce two results in response to flight searches: one showing the fare, and another showing the price of the fare plus “the cost of baggage charges that traditionally have been included in the price of a ticket.” It also considered requiring fees for advance seat assignments to be included in that second price.

That proposal was in its NPRM. But when issuing its final new “passenger protection” rules last April, the DOT ultimately decided that a “two-fare” display would be too confusing for travelers. The DOT also said it agreed that “each traveler is unique with regard to what ancillary services he or she needs or wants on a particular flight, and therefore one ‘all-inclusive’ price that includes baggage and a seat assignment may not be helpful to most passengers.”

The DOT made that decision just weeks after Spirit unveiled its plans to implement a carry-on fee,. The DOT referred to carry-on fees in its final rule, which did include requirements for greater airline disclosure of bag fees and changes in bag fees.

Schumer’s argument to LaHood is that carry-on fees merit different consideration than checked bag fees because it is much more difficult for customers to avoid taking a carry-on. “Bringing a carry-on bag is effectively a compulsory part of flying,” he argued.

“For nearly all airline passengers, a carry-on bag fee would effectively represent an increase in the cost of the flight,” he wrote in his letter. “While it is the airline’s prerogative to decide how much to charge its consumers for a flight, my concern is that consumers not be misled into paying more for a flight than they otherwise would have paid had they known the total cost of that flight upfront.”

Airlines for America, however, criticizes Schumer’s proposal as “unnecessary regulation.” Airlines already provide details on fares and costs of other optional services prior to purchase, it says.