United Airlines said that a software update triggered a glitch that forced it to halt departures nationwide on Tuesday, temporarily impacting one of the nation's biggest carriers on a busy travel day.

The airline said that it experienced a "systemwide technology issue" forcing it to temporarily ground its flights on Tuesday afternoon.

“A software update caused a widespread slowdown in United’s technology systems,” United said in a statement. The airline said it was not a cybersecurity issue.

In a statement to Spectrum News, a spokesperson for the Federal Aviation Administration said that United asked the agency to pause departures nationwide. 

The ground stop lasted a little more than an hour. It did not affect planes already in the air, per the airline.

By late afternoon Tuesday on the East Coast, United had canceled only seven flights, well below its average of about 16 per day over the busy Labor Day weekend, per FlightAware.

However, more than 350 United flights were delayed — 13% of the carrier’s schedule, far more than rivals American, Delta and Southwest — on a day that many holiday vacationers were expected to fly home.

Southwest Airlines had a similar outage in April that grounded all departing flights for about an hour and caused more than 2,000 flights to be late.

The FAA caused all U.S. departures to be halted briefly in January when a system used to alert pilots to safety hazards failed. The agency blamed a contractor that it said accidentally deleted files while synchronizing the alert system and its backup.

Transportation Secretary Pete Buttigieg wrote in a post on X, formerly known as Twitter, that he was "aware" of the issue and that the FAA was "currently receiving more information about the cause and scope of the issue."

"DOT will make sure [United] meets its obligations to affected passengers," he added.