Debates over the Trump administration’s immigration enforcement agenda have led to a partial government shutdown affecting agencies under the Department of Homeland Security (DHS) umbrella.

Among the agencies affected is the Transportation Security Administration (TSA), which went into shutdown on Feb. 14, creating uncertainty for air travelers.

Travel and aviation experts say lines at U.S. airports could increase the longer the partial shutdown endures, adding another layer of frustration for travelers trying to plan during the winter season.

It’s unclear when the agencies will reopen as negotiations between the Democrats and White House on DHS funding remain stalled days into the partial shutdown.

Here is a look at how the shutdown may impact air travel nationwide.

TSA

Roughly 95 percent of TSA employees are deemed essential and will still be required to screen passengers and their luggage at the nation’s commercial airports. They will be working without pay during the shutdown.

These employees similarly worked without pay during last year’s 43-day government shutdown, which caused historic flight cancellations and delays that lasted for weeks.

With last year’s shutdown still in the rear-view mirror, the prospect of working again without pay may prompt some employees to call out sick or request unscheduled leave.

“Twelve weeks later, some are just recovering from the financial impact of the 43-day shutdown. Many are still reeling from it,” Ha Nguyen McNeill, TSA deputy administrator, said during a congressional hearing on Feb. 11.

“In addition to the grave impact on the TSA workforce without budget certainty, we are at risk of critical technology deployments being pushed even further out.”

Impacts on Air Travel

Since the Federal Aviation Administration’s (FAA) air traffic controllers are not impacted by the shutdown, there’s a lower risk of the widespread flight cancellations seen last year.

However, the previous shutdown also saw air travel disruptions triggered by the TSA’s lapse in funding.

Roughly a month into that shutdown, the agency had to temporarily close two security checkpoints at Philadelphia International Airport, delaying travelers.

Wait times are expected to be longer at smaller airports with limited security checkpoints, especially if significant numbers of TSA officers are taking unscheduled absences.

Rich Davis, senior security adviser at risk mitigation company International SOS, said airlines could opt to delay some departures to allow additional time for passengers to clear screening checkpoints.

TSA employee shortages could also delay checked bag screening before luggage is loaded onto planes.

Airport websites may display security line wait times, which can help travelers determine if they need to arrive earlier to make their flights.

The shutdown could further disrupt air travel as the country enters the busy spring break travel season, U.S. Travel, Airlines for America, and the American Hotel & Lodging Association warned in a joint statement.

“Travelers and the U.S. economy cannot afford to have essential TSA personnel working without pay, which increases the risk of unscheduled absences and call-outs, and ultimately can lead to higher wait times and missed or delayed flights,” their statement said.

The Associated Press contributed to this report.