Holiday travel may be more chaotic than ever this year, transportation experts say

Holiday travel may be more chaotic this year, experts warn, as looming vaccination deadlines threaten airline and airport staffing.

Forty percent of the Transportation Security Administration (TSA) workforce hasn't received a single dose of the COVID-19 vaccine, the agency said Thursday, and they only have until Nov. 22 to get fully vaccinated.

"Even if they get half of that done by Thanksgiving, that leaves 20% not available to work," aviation expert Henry Harteveldt told ABC News. "Something's going to have to give. I'm really worried."

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TSA said it is currently developing contingency plans, but anticipates "that the vast majority of TSA employees will get vaccinated."

Several major U.S. airlines are also grappling with the fast-approaching vaccine requirement deadlines.

American Airlines and Jet Blue are requiring U.S.-based workers to provide proof of vaccination the day before Thanksgiving.

"This is happening at perhaps the most difficult time ever," spokesperson for the Allied Pilots Association Capt. Dennis Tajer said. "We have a very high volume of flying and it's created a lot of uncertainty about the holiday travel period. Now you have some unknown quantity of pilots that that may go away and go through termination."

Out of the 14,000 American pilots Tajer's union represents, 4,000 pilots remain unvaccinated.

"We've heard about all the staffing issues that happen," Tajer said. "It's not just on the flight deck in the cockpit, it's happening throughout corporations everywhere."

Southwest's operational meltdown last weekend served as a potential warning of what's to come this winter.

Tens of thousands of passengers were stranded at U.S. airports due to the more than 2,000 flight cancelled within three days.

The airline blamed the multi-day mess on air traffic control issues, bad weather and "other external constraints."

On Thursday, Southwest said it's going to hire more than 5,000 employees by the end of the year to mitigate future issues and has 50% of the goal met.

With airlines booking their flights to 100% capacity, experts are concerned there is no wiggle room left in the system to recover if a major airline melts down during the busy travel season.

"The chaos that is the Thanksgiving and Christmas holiday travel season will be even more chaotic this year," Harteveldt said.

He recommends traveling on off-peak days and to book on the airline that has the most flights to your destination, even if that's not the airline you normally fly.

"Take the earliest possible departure in the morning that you can, because it gives you more leeway if something goes wrong," he added.

ABC News' Sam Sweeney and Victor Oquendo contributed to this report.