Several travel advocacy organizations — including the Business Travel Coalition, Consumer Federation of America, and National Consumer League — wrote a letter asking Sens. Mitch McConnell and Harry Reid to support the inclusion of the Forbid Airlines from Imposing Ridiculous (FAIR) Fees Act as an amendment to the Federal Aviation Administration Reauthorization Act of 2016.

Sponsored by Sens. Ed Markey and Richard Blumenthal, the FAIR Fees Act would prohibit airlines from charging cancellation, baggage, or other ancillary fees that are “unreasonable or disproportional to the costs incurred by the air carrier,” under standards set by the Department of Transportation (DOT).

The FAIR Fees Act doesn’t look to re-regulate the airlines, but it serves to remedy a systemic violation of the free market system that has been pointed out by both the DOT and the Department of Justice (DOJ), according to the letter.

In 2015, U.S. airlines collected $10.8 billion in ancillary fees, an increase of 24% since 2014, according to a survey by IdeasWorksCompany.

These add-on fees have generated more complaints among consumers. From 2014 to 2015, consumer complaints to the DOT increased by 30%, according to the DOT. And complaints about airline fares are the fastest-growing category of complaints to the DOT (97.93% year-over-year increase), according to the DOT’s Air Travel Consumer Report from February 2016.

“The FAA Reauthorization Act is an important opportunity for you and your Senate colleagues to protect the millions of consumers who depend on the airline industry to provide an affordable, dependable, and safe travel experience,” the letter stated. “The FAIR Fees Act would do much to help reign in the industry’s increasing reliance on ancillary fees, which are unfairly squeezing the pocketbooks of the flying public. We urge you to support this common sense, pro-consumer bill.”