US aviation officials have reported delays in air travel because of a "slight increase in sick leave" at two East Coast air traffic control facilities.
The delays come as a partial government shutdown threatens to undermine the nation's air travel system.
Air traffic controllers and airport security agents have been working without pay since the federal shutdown began in December, and high absentee rates raise the possibility of long airport queues, or even worse.
White House spokeswoman Sarah Sanders said Donald Trump has been briefed on the delays and "we are monitoring the ongoing delays at some airports".
"We are in regular contact with officials at the Department of Transportation and the FAA (Federal Aviation Administration)," Ms Sanders said in a statement.
New York governor Andrew Cuomo wrote a letter to the president earlier on Friday saying the shutdown is impacting safety and security at airports and putting travellers at risk.
FAA spokesman Gregory Martin said it had augmented staffing, rerouted traffic and increased spacing between planes as needed.
The staffing problems were at air traffic centres in Jacksonville, Florida, and a Washington DC site that controls high-altitude air traffic over seven states.
"The results have been minimal impacts to efficiency while maintaining consistent levels of safety in the national airspace system," Mr Martin said.
LaGuardia Airport in New York and Newark Liberty International Airport in New Jersey were both experiencing at least 90-minute delays in take-offs today.