– As airport and government officials search for a fix for the long airport security lines plaguing airports in U.S. cities, one possible culprit has come into focus: baggage fees.

Some say fees for checked bags prompt travelers to carry on more bags, all of which have to be screened at security checkpoints.

Two U.S. senators have proposed that airlines stop charging baggage fees this summer. But airlines are loathe to lose the hundreds of millions in revenue they collect from baggage fees.

In a letter to airline executives, Sens. Richard Blumenthal, D-Conn., and Edward Markey, D-Mass., acknowledged that many factors play into the lines, including staffing cuts for federal screeners and tighter security protocols after lapses revealed in tests.

But they told the executives: “You can take some action right away. … Suspend bag fees for the summer.” The letter, citing Transportation Security Administration information, said that checkpoints serving airlines with checked baggage fees handled 27 percent more roller bags than checkpoints for carriers that do not.

A spokesman for Delta Air Lines, which charges $25 for a first checked bag, said the senators’ request would entail a “considerable change to the business model.”

“We don’t think that shifting that traffic to the baggage check area … would really help alleviate a lot,” said the spokesman, Michael Thomas.

He said that Delta is working with TSA on strategies to cut wait times, including contributing staff to help manage lines and paying for new lanes aimed at processing passengers faster.

In the third quarter of 2015, Delta collected nearly $237 million in baggage fees. American Airlines took in $292 million, while United Airlines had more than $184 million in bag fee revenue.

Southwest Airlines does not charge fees for the first two checked bags.

While senators can ask airlines to waive bag fees, “I don’t think you’re going to see that happen,” said Bill Rinehart, founder of DUFL, a personal valet service that ships, cleans and stores business wear for travelers.

“It’s a massive revenue stream. They’re all private businesses. I’m not sure why they would feel like they need to do that for the government,” he said.