The Federal Aviation Administration briefly halted flights into New York’s LaGuardia Airport on Friday morning, with ripple effects elsewhere on the East Coast, because of a shortage of air traffic controllers amid a partial shutdown of the federal government that has forced them to work without pay since Dec. 22.

“We have experienced a slight increase in sick leave at two facilities,” an FAA spokesperson said in a statement. “We’ve mitigated the impact by augmenting staffing, rerouting traffic, and increasing spacing between aircraft when needed.”

The spokesperson said the two facilities were the Washington Air Route Traffic Control Center in Leesburg, Va., which maintains flight separation and sequences arrivals and departures on some of the busiest routes on the East Coast, and a center in Jacksonville, Fla., that handles the same job for a broad swathe of the Southeast.

The staffing shortfalls led the FAA to order a ground stop to planes bound for LaGuardia shortly before 10 a.m., with flights resuming at a slower rate later in the morning. According to an FAA airport status website, arriving flights at LaGuardia have been delayed by an average of 86 minutes, while departing flights were experiencing gate hold and taxi delays between 15 minutes and a half hour.

Departures have been impacted at East Coast airports that serve LaGuardia, including Orlando International, Miami and Philadelphia. Weather-related arrival delays at Newark International of 46 minutes to an hour were also causing disruption.

The staffing shortfall at the air traffic control centers comes after federal workers missed a second paycheck Friday due to the shutdown. About 420,000 workers deemed essential have been instructed to work without pay, including air traffic controllers and security screeners from the Transportation Security Administration. TSA workers have been taking sick leave in rising numbers, leading to longer security lines at some airports, but this is the first time that absences of air traffic controllers have disrupted flights.

The TSA said that 7.5% of its airport screeners were absent from work Wednesday, up from 3% on the same day a year ago.

“This is exactly what [we] and other aviation unions have been warning would happen,” Sara Nelson, president of The Association of Flight Attendants-CWA, said in a statement Friday. “Do we have your attention now, Leader McConnell? All lawmakers?” 

Aviation unions warned in a joint statement Wednesday that the government shutdown was undermining safety. “In our risk averse industry, we cannot even calculate the level of risk currently at play, nor predict the point at which the entire system will break,” said the statement from unions representing air traffic controllers, pilots and flight attendants. “It is unprecedented.”

Staffing among air traffic controllers was already at a 30-year low, according to the National Air Traffic Controllers Association, and the shutdown has forced the FAA to halt hiring and shutter its training academy.