Hollywood Burbank Airport in Southern California was without air traffic controllers for more than five hours on Monday evening due to the ongoing government shutdown.

Between 4:15 p.m. and 10 p.m., the airport’s control tower was completely unmanned, according to the Federal Aviation Administration. Planes had to rely on a team operating near San Diego to manage departures and arrivals.

Nearly 25% of arriving and departing flights at the airport were delayed Monday, according to flight tracking website FlightAware.

Despite being essential employees, air traffic controllers are required to work during a government shutdown, yet they do not receive pay for their hours.

“So now what they think about as they’re controlling our airspace, is, ‘How am I going to pay my mortgage? How do I make my car payment?” Transportation Secretary Sean Duffy stated at a press conference on Monday. “If someone has to take sick leave to drive Uber to make the difference, those are decisions they’re going to make themselves.”

Control towers in Phoenix and Denver, two of the nation’s busiest airports, also reported significant staffing shortages Monday.

By Tuesday morning, normal operations had resumed at Burbank Airport, the Los Angeles Times reported.

In the past, air travel issues have been a factor in ending a government shutdown. In January 2019, a 35-day shutdown concluded when the FAA had to limit flights into several major airports due to a high number of air traffic controllers taking sick leave.