DALLAS (AP) — Southwest Airlines planes were briefly grounded nationwide Tuesday for what the airline called an intermittent technology issue, leading to more than 2,200 delayed flights just four months after the carrier suffered a much bigger meltdown over the Christmas travel rush.

The hold on departures was lifted by mid-morning Eastern time, according to Southwest and the Federal Aviation Administration, but not before traffic at airports from Denver to New York City backed up.

“Southwest has resumed operations after temporarily pausing flight activity this morning to work through data connection issues resulting from a firewall failure,” the Dallas-based airline said in a prepared statement. “Early this morning, a vendor-supplied firewall went down and connection to some operational data was unexpectedly lost.”

Southwest urged customers to check on their flight status “and explore self-service options” for travel as the airline worked on restoring its operation.

By late afternoon on the East Coast, more than half of all Southwest flights were delayed, and the airline accounted for half of all delays nationwide. On the positive side, Southwest had only about a dozen flights canceled, roughly in line with other major airlines, according to FlightAware.

Transportation Secretary Pete Buttigieg retweeted an FAA post about the ground stop, adding, “We are here to ensure passengers have strong protections when airline failures like this affect their plans.” He referred travelers to a Transportation Department checklist of passenger rights, and his press secretary noted that “no other airlines experienced disruptions.”

Tuesday’s delays added to the picture of an airline that has struggled more than most with technology issues.

“It was a 17-minute ground stop. This will have no long-lasting affect on Southwest’s reputation,” said Henry Harteveldt, a travel analyst with Atmosphere Research Group. “What matters now for Southwest is getting to the cause and doing all it can to ensure incidents like this don’t occur again.”

Rob Britton, a former American Airlines executive who teaches crisis management at Georgetown University, said the damage from Tuesday’s incident will be minor but will add to the erosion of Southwest’s image. He said Southwest has underinvested in technology while growing rapidly, and it suffers from an “insular culture” that “keeps them from looking outside for solutions.”

In December, Southwest canceled nearly 17,000 flights in a 10-day stretch around Christmas — wrecking holiday travel plans for well over 2 million people — when a winter storm shut down its operations in Denver and Chicago and the airline’s system for rescheduling pilots and flight attendants was overwhelmed.

Those cancellations cost the airline more than $1 billion and led to an ongoing Transportation Department investigation and a congressional hearing during which lawmakers complained that Southwest provided little or no help to stranded travelers.

Sen. Maria Cantwell, D-Wash., who led that hearing, said Tuesday’s breakdown “is another demonstration that Southwest Airlines needs to upgrade their systems and stop the negative impacts to individual travelers.”

The airline’s unions have said they warned management about problems with the crew-scheduling system after a previous meltdown in October 2021.

CEO Robert Jordan has embarked on a campaign to repair the airline’s damaged reputation. Southwest said last month it would add deicing equipment and increase staffing during winter weather that is cold enough to limit the amount of time that ground workers can stay outside.

Shares of Southwest Airlines Co. fell Tuesday nearly 1% while its closest rivals — American, Delta and United — all gained at least 1.5%.