U.S. airline bosses are stepping up their criticism of the partial government shutdown, warning that the closing threatens to snarl air travel as it drags into its 34th day.

"We are close to a tipping point as employees are about to miss a second paycheck," JetBlue Airways Corp. Chief Executive Officer Robin Hayes said on a conference call Thursday with analysts and investors. "The longer this goes on, the longer it will take for the nation's air travel system to rebound."

CEOs at larger carriers backed him up, with American Airlines Group Inc.'s Doug Parker warning of "long lines" and "delayed airspace." Southwest Airlines Co. said it lost out on as much as $15 million (¥1.6 billion) in sales this month because of the shutdown.