All United Airlines flights in the U.S. were grounded Wednesday morning due to "automation issues," the Federal Aviation Administration reported.

3,500 flights United flights are affected worldwide.

"Automation issues" are another way of saying there are problems with the back-end software and hardware United is using, according to the Verge. The current grounding affects "mainline" aircraft only, according to the FAA.

There's no word on when the computer problems will be fixed.

Passengers are tweeting about the chaos and lines at the airports.

In early June a software glitch grounded United aircraft for around 30 minutes, but the length of this grounding has already exceeded June's.

Updated at 10 a.m.: FAA reports that United Airlines flights are no longer grounded. Passengers are re-boarding planes.

Updated at 10:30 a.m.: Passengers are reporting that the boarding pass scanning system is still not working, so agents are writing information out by hand.

Updated at 11:30 a.m.: "We are recovering from a network connectivity issue this morning and restoring regular flight operations," United Airlines said in a statement. "We will have a waiver available at for customers who are able to change their flight plans."