LAS VEGAS (KLAS) — The Federal Aviation Administration has lifted the ground stop for Southwest Airlines but passengers may feel the delays throughout the day.

Tuesday morning, FAA said a pause of the airline’s departures was requested by the airline due to an internal technical issue. It caused the immediate delay of more than 1,500 flights nationwide, according to Flight Aware which is a website that tracks flights all over the world. Southwest did cancel some of its morning flights out of Reid International Airport to Southern California cities.

As of 8 a.m., more than 1,500 Southwest flights were showing delayed. After the pause was lifted, the nationwide delays dropped to 200.

Southwest did post apologies in response to the numerous travelers who took to Twitter upset about the ground stop.

“Technical errors are unexpected and inconvenient for all, and you have our sincere apologies.”

The airline said a firewall supplied by a vendor went down early Tuesday, and connection to some operational data was lost. 

Southwest canceled nearly 17,000 flights over the Christmas holiday due to bad weather and its crew-scheduling system becoming overwhelmed. Those cancellations cost the airline more than $1 billion and are currently being investigated by the Transportation Department.