April 21, 2013 -- Air travel is likely to become even more frustrating than usual, starting today. The Federal Aviation Administration has begun furloughs resulting from mandatory budget cuts for some of its 47,000 agency employees.
It's unclear how many employees are already affected by so-called sequestration, the automatic federal spending cuts that kicked in this year after Congress failed to reach a deal to reduce the national deficit.
The bottom line is that travelers are faced with the real possibility of hours-long delays as air-traffic controllers -- there are 15,000 of them -- begin to take unpaid leave, the FAA says.
American Airlines has said that some of the nation's busiest airports will most likely be affected by the FAA cuts: JFK in New York; Newark; Chicago's O'Hare; LAX in Los Angeles; and New York's LaGuardia.
This is a relatively slow time of year for air travel, so any fallout would likely intensify in the summer, when weekends rival Thanksgiving for busiest air-travel time, travel experts say. Throw in unpredictable summer thunderstorms, and there's reason for worry, according to the National Air Traffic Controllers Association.
But there are already signs of trouble:
@akashgoyal tweeted today, "Is our gate agent for real? She's blaming a 45-min delay to my flight on 'government cut-backs' on overhead announcements."
The Metropolitan Washington Airports Authority has picked up early signs of delays: Ronald Reagan National is reporting today "several minute increased wait times at TSA security screening," the authority says.
The National Air Traffic Controllers Association has reported no substantial holdups today with the light travel and good weather.
Airlines for America, which represents most domestic carriers, filed a lawsuit against the FAA Friday in an attempt to block controller furloughs.
In a statement issued by the carrier Saturday, customers were urged to check their flight status before coming to the airport today.
"Unfortunately, the FAA has not yet provided specific details to the airlines, making it difficult to communicate exactly how customers will be affected," American said. "However, we will make every effort to communicate with our customers as information becomes available."
Ordered to find a way to cut $637 million from the agency's budget, the FAA is forced to schedule one furlough day every two weeks for an unspecified number of employees, which officials say will mean fewer takeoffs and landings.
As ABC News reported Friday, Department of Transportation Secretary Ray LaHood at a news conference warned that passengers could see "a wide range of impacts across the system," adding that "safety is not up for negotiation during the sequester" and "will not be compromised in anything that we do."
"This is not what we signed up for," LaHood added. "[The sequester] is a dumb idea."
ABC News' Genevieve Shaw Brown contributed to this story.