Southwest Airlines fliers face a second day of slow check-ins due to a technical glitch.

The glitch, which began on Sunday, prevents agents from issuing tickets and boarding passes, forcing them to be created by hand. Travelers are advised to arrive at the airport at least 2 hours ahead of time to help minimize delays which caused long check-in lines at some airports around the country including Newark, LaGuardia, JFK and Philadelphia..

"We’re continuing to use back-up systems around the country to check-in customers arriving at our airports without printed or mobile boarding passes," reads an update on the airline's website. "Intermittent performance issues continue impacting our in-airport Customer Service technology systems and across our online platforms.

Representatives for Southwest did not say what caused the problem or how long it would take to resolve. Spokesman Brad Hawkins said there was "absolutely no indication now" that the problems were the result of hacking.

According to the airline, 450 of 3,600 scheduled flights on Sunday were delayed.