American Airlines' chief operating officer, Robert Isom, said that executives from all the major US carriers met with the head of the TSA and the US Department of Homeland Security last week to air their grievances over the situation.

Isom wrote about the meeting in a letter to employees, dated May 18.

"Two words: TSA lines," Isom wrote in the letter. "Right now those words evoke frustration from all of us, as well as our customers who continue to miss flights due to lines that are literally out the door."

The delays — which American Airlines attributes to severe understaffing on the part of the TSA — have been growing for months but reached new heights last weekend when passengers at Chicago's O'Hare International airport were left stranded after security lines exceeded three hours.