The holiday travel rush kicked off this week, but a looming government shutdown could lead to longer TSA wait times at the airports and impact ATC hiring if the shutdown lasts for long.

Airlines for America, an airline trade organization, anticipates a record-breaking winter holiday season, with more than 54 million passengers expected to fly on U.S. carriers.

Here’s what would be affected if lawmakers don’t come to an agreement on funding before Friday night’s deadline.

TSA

Transportation Security Administration (TSA) workers at airport security checkpoints are considered “mission essential” and will be required to work without pay if there is a government shutdown.

A TSA spokesperson told ABC that 59,000 of the agency’s 62,000 employees are considered essential workers and will continue to work. The agency said that while it is prepared to manage the high volume of travelers this holiday season, an extended shutdown would lead to longer airport wait times.

The TSA expects to screen 40 million travelers from Dec. 19 through Jan. 2, a 6.2% increase from last year.

Although travelers could face longer wait times at airports during an extended government shutdown, commercial airlines are not expected to be affected and should continue to operate.

Those traveling internationally shouldn’t face issues as domestic consular operations, including passport and visa services, will remain functional as they are fee-funded operations, according to the State Department’s contingency plan. U.S. embassies and consulates abroad will also continue operating under the plan.

ATC

Many air traffic controllers who are members of the National Air Traffic Controllers Association (NATCA), are required to work without pay during a shutdown.

This would mean working overtime with six-day work weeks and 10-hour shifts, as other aviation safety professionals are furloughed.

According to the Department of Transportation’s shutdown contingency plan, over 12,000 air traffic controllers would be expected to work without pay during a shutdown. The contingency plan also states that out of 46,277 Federal Aviation Administration (FAA) employees, more than 17,000 are expected to be furloughed.

During a shutdown, the FAA cannot hire or train air traffic controllers. It would force the FAA to close its ATC training facility in Oklahoma. It would also take some trainee controllers working at airport towers off the job.

This year, the FAA exceeded its hiring goal by adding 1,811 air traffic controllers — the largest number in nearly a decade. However, the agency remains 3,000 air traffic controllers short of its staffing needs, and a government shutdown could set back the progress made.

“We’ve seen a gap that has opened up over many years for the level of staffing — we finally have that headed in the right direction,” Secretary Buttigieg said during a press conference last year addressing the potential impact of a government shutdown on air traffic controllers. “But that can’t happen if we get stopped in our tracks with training. At the end of the day that means more shortages and more outages, and that can contribute to cancellations.”

A coalition of aviation stakeholders representing industry and labor has sent a letter to leaders in the Senate and the House, urging immediate action to avert a government shutdown.

“During a shutdown, many FAA employees are furloughed, meaning that they cannot perform their duties that support aviation safety, aircraft certification and the integration of new entrants. The ensuing backlogs cause further delays in these critical FAA services long after funding resumes,” the letter stated.

“While air traffic controllers will continue to work without pay, many of the employees who support them are furloughed, and the programs that the FAA uses to review and address safety events are suspended. To remain the world leader in aviation, we must continue to strive to improve efficiency and further mitigate risk,” it continued.