Federal Aviation Administration has confirmed that all domestic flights will be grounded until Wednesday, January 11, at 9:59 a.m.

According to the agency, the Notice to Air Missions System (which sends important notices to pilots) is currently being reloaded. Numerous airlines reported problems when they were unable to give clearance for flights to leave.

The FAA continues to work to restore the Notice-to-Air Missions system after an outage. Although some functions are starting to return online, National Airspace System operations remain limited,” tweeted the agency just before 7:01 a.m.

The FAA responded to the tweet with a follow-up 20 minutes later. It stated that all domestic flights would now be grounded in order to “allow agency to validate integrity of flight information and safety information.”

American Airlines, United Airlines and Southwest Airlines all confirmed that the flight operations would be affected by the problem. United Airlines stated that all domestic flights were “temporarily delayed” while the FAA provides more information.

Transport Secretary Pete Buttigieg stated Wednesday morning that he was “in touch” with the FAA and “working to resolve this matter quickly.”

“I spoke with FAA about the outage that affected a critical system to provide safety information to pilots. FAA is working quickly and safely to resolve the issue so that air traffic can return to normal operations. Buttigieg tweeted shortly after 7:15 a.m.

According to FlightAware, more than 100 flights from the U.S. were cancelled and over 1,200 delayed Wednesday.