Staffing shortages led to more flight delays at airports across the U.S. on Tuesday as the federal government shutdown stretched into a seventh day, while union leaders for air traffic controllers and airport security screeners warned the situation was likely to get worse.

The Federal Aviation Administration reported staffing issues at airports in Nashville, Boston, Dallas, Chicago, and Philadelphia, and at its air traffic control centers in Atlanta, Houston, and the Dallas-Fort Worth area. The agency temporarily slowed takeoffs of planes headed to the first three cities.

Despite the challenges, about 92% of the more than 23,600 flights departing from U.S. airports as of Tuesday afternoon took off on time, according to aviation analytics firm Cirium. However, the risk of wider impacts to the U.S. aviation system is growing daily as federal workers whose jobs are deemed critical continue working without pay. Analysts warn that prolonged shutdowns could severely affect travel plans leading up to Thanksgiving.

Transportation Secretary Sean Duffy noted an uptick in air traffic controllers calling out sick, raising alarms about operational capacity. When there aren’t enough controllers, the FAA must reduce the number of takeoffs and landings to maintain safety, which in turn causes flight delays and possible cancellations, Duffy explained.

With concerns escalating, some airports have initiated support measures for federal workers, including food vouchers and emergency services. Tampa International Airport is reportedly set to assist its 1,100 federal employees through various programs, ensuring they can continue their essential work during these challenging times.