NEWARK, New Jersey — A temporary ground stop was issued for incoming flights at Newark Liberty International Airport on Thursday morning because of Air Traffic Control communication issues.

ATC controllers in the center told ABC News they lost their radio frequencies.

Officials said incoming flights to Newark and Teterboro airports were ground-stopped due to equipment issues at the FAA until 12:30 p.m. The ground stop is over, but delays were still averaging more than two hours at 1 p.m.

Departing flights did not appear to be impacted.

A spokesperson with United Airlines described the ground stop as a “glitch.”

This is the second outage for controllers at the Philadelphia ATC center that handles air traffic control for Newark airspace in the last 24 hours.

There was another outage between 6:30 and 7:30 p.m. Wednesday where audio wasn’t coming in clear between planes and controllers for a brief time.

Controllers at Newark were warned that frequency issues could happen any time over the next 24 hours, an on-duty controller told ABC News.

The FAA is reducing flights into Newark to 28 per hour until at least Friday compared to the previous 34 an hour. Arrivals are also being spaced out about to 20 miles apart as they approach the airport.

The issues come as the busy Labor Day travel weekend is getting underway.

After Air Traffic Control issues this spring, the FAA reduced the number of flights going in and out of the airport through the summer.