The Homeland Security shutdown that began early Saturday is straining airport security operations nationwide as the agency responsible for screening passengers and bags, the Transportation Security Administration, is expected to have officers working without pay. For travelers with reservations, it is reviving memories of the 43-day shutdown last year, which led to major flight cancellations and long delays.

Transportation Security Administration officers are expected to keep working while lawmakers remain without an agreement on DHS’s annual funding, and the TSA workforce also will be dealing with the aftereffects of the earlier, record shutdown that ended Nov. 12. Aviation experts and risk managers said disruptions could appear faster than many travelers expect as the TSA workforce has both operational and personal reasons to be stressed by an ongoing funding lapse.

The shutdown is taking effect even though other federal agencies remain funded through Sept. 30, which could reduce some of the worst-case air-travel disruptions seen last year. According to the department’s contingency plan, about 95% of TSA workers are deemed essential personnel and are required to keep working, but lawmakers and TSA employees face the prospect of operating without pay while negotiations continue.

In previous shutdown episodes, air-travel disruptions tended to build over time rather than overnight. Last year, for example, about a month into the shutdown, TSA temporarily closed two checkpoints at Philadelphia International Airport and, the same day, the government ordered airlines to reduce domestic flight schedules. This time, experts said the immediate problem could be variability in screening availability—if even a small number of TSA officers are absent at a given airport, wait times at a single checkpoint can worsen quickly.

John Clark, arriving at Detroit Metropolitan Airport from a business trip in Mississippi, said he was impacted by the earlier shutdown and is worried about getting home. “You might not be able to get home if you’re already out, or it might delay if you worked all week and you’re trying to get home,” said Clark, who frequently travels for his job balancing machines. John Rose, chief risk officer for global travel management company Altour, said the strains could surface more quickly this time because TSA staff are also “remembering the last shutdown.”

Rose also said it is difficult to predict when or where security screening snags might pop up during a shutdown because disruptions can be localized. He and other experts urged travelers to plan around the possibility of longer lines, including arriving early and building in extra time to clear security—especially at smaller airports where a single checkpoint can become a bottleneck if staffing is thinner than normal.

Rose said travelers should not wait until the day of their flight to check security line wait times posted online by airports. “You may look online and it says two-and-a-half hours,” he said. “Now it’s two-and-a-half hours before your flight and you haven’t left for the airport yet.” He also urged passengers to pay close attention to prohibited items when packing so that screening delays are less likely to be triggered.

At the airport, Rose advised travelers to “practice patience and empathy,” pointing to both the pay situation and the possibility of reduced staffing. “Not only are they not getting paid,” he said of TSA agents, “they’re probably working with reduced staff and dealing with angry travelers.” Rich Davis, senior security adviser at risk mitigation company International SOS, said flight delays also remain possible because airlines might hold departures to wait for passengers to clear screening, and because shortages of TSA officers could slow checked-luggage screening behind the scenes.

For some travelers, the main concern is how quickly the shutdown could affect their travel dates. Burnest R. Green, who flew to Detroit from Phoenix for his sister’s 70th birthday, said he wants the shutdown ended before he flies back in over a week’s time. “I just hope that things start to get better before they get any worse,” he said.

Negotiations have continued without a deal by the end of the week, when senators and members of Congress were set to leave Washington for a 10-day break. The White House and Democratic lawmakers failed to reach an agreement before that deadline, and Democrats have said they will not help approve more DHS funding until new restrictions are placed on federal immigration operations after the fatal shooting of Alex Pretti and Renee Good in Minneapolis last month.

In a joint statement, U.S. Travel, Airlines for America and the American Hotel & Lodging Association warned that the shutdown threatens to disrupt air travel as the busy spring break travel season approaches. “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,” the statement said.