• Lawmakers in the House voted down a short-term spending bill on Thursday, raising the chances for a government shutdown.
• If no deal is reached, the shutdown could begin 12:01 a.m. ET on Saturday.
• Air traffic controllers and TSA agents are considered essential employees, though they could end up working without a paycheck.

A government shutdown is looming just as the peak holiday travel season gets underway.

Lawmakers have been at an impasse and on Thursday voted down a short-term bill, which was backed by President-elect Donald Trump, to continue to fund the U.S. government. A shutdown could begin as early as 12:01 a.m. ET on Saturday if no deal is reached.

Hundreds of thousands of government employees would be furloughed if Congress fails to pass a spending bill.

A government shutdown could cost the U.S. travel industry $1 billion per week, estimated the U.S. Travel Association, which represents major hotel groups and others.

"It's hard to see how anyone in Congress wins if they force TSA workers, air traffic controllers, and other essential employees to work without pay during one of the busiest travel periods of the year," Geoff Freeman, the group's president, said in a statement on Friday.

What does this mean for air travel?

Commercial airplanes are still scheduled to fly, even given the chance of a shutdown.

Airlines are forecasting the busiest year-end holiday season on record. The Transportation Security Administration expects its officers to screen more than 40 million people during the holidays through Jan. 2. United Airlines alone said it will fly 9.9 million people between Dec. 19 and Jan. 6, up 12% over last year.

The government deems the more than 14,000 air traffic controllers and close to 60,000 TSA agents essential, which means they would continue working, though they wouldn't be paid during the shutdown.

Prepare for longer lines?

TSA officers "would continue working without pay in the event of a shutdown," the agency's administrator, David Pekoske, said Thursday on social media platform X.

"While our personnel have prepared to handle high volumes of travelers and ensure the security of our transportation systems, an extended shutdown could mean longer wait times at airports," the TSA said in a statement Friday.

What happened last time?

The last time the government shut down, it stretched for more than a month from late 2018 through early 2019.

Callouts from a few air traffic controllers in the highly congested airspace along the U.S. East Coast snarled air traffic during that shutdown. Then-President Trump and lawmakers reached a deal shortly after that to end the shutdown, the longest funding lapse in U.S. history.

Congestion has vexed airline leaders. Meanwhile, the Federal Aviation Administration is once again without a permanent administrator after FAA chief Mike Whitaker, who was appointed by President Joe Biden last year, said he will step down Jan. 20, when Trump takes office.

Modernization of air traffic control and hiring more controllers should be the next FAA administrator's priority, Delta Air Lines CEO Ed Bastian told CNBC earlier this week.