Lawmakers on Capitol Hill will investigate a Federal Aviation Administration outage that caused thousands of flight delays early Wednesday morning as part of their discussions of upcoming FAA reauthorization legislation.

The FAA on Wednesday announced on Twitter an outage of its information and operations notification system, called the Notice to Air Missions system, leading the agency to call a “ground stop” that brought over 4,000 delays and 800 cancellations in the U.S., according to FlightAware data. 

Although the agency lifted the ground stop by 9 a.m., thousands of flights remain delayed across the country. Alyssa Black, a United Airlines passenger scheduled to fly out of Dulles International Airport on Wednesday morning, said her gate agents announced the FAA “has zero communication” with them and that agents were checking Twitter for updates on the outage. “They can’t tell us how long our flight is being delayed,” Black said.

Senate Majority Leader Charles E. Schumer, D-N.Y., tweeted that he has been in contact with Transportation Secretary Pete Buttigieg, who assured him that “FAA is working as quickly as possible to restore their computer system so flights can safely resume and are looking into what caused this stoppage.”

Although it’s not clear yet what caused the outage, White House Press Secretary Karine Jean-Pierre also tweeted that there is “no evidence of a cyberattack at this point,” but President Joe Biden called for a “full investigation into the causes.”

“Aircraft can still land safely, just not take off right now,” Biden told the press pool Wednesday morning. “They don’t know what the cause of it is. They expect in a couple of hours they’ll have a good sense of what caused it and will respond at that time.”

But the outage adds yet another FAA reauthorization topic for lawmakers to consider that’s inspired by recent airline chaos — a charge that both Democrats and Republicans have taken up. 

Senate Commerce, Science and Transportation Chair Maria Cantwell, D-Wash., said in a statement that the committee will investigate what caused the outage and “how redundancy plays a role in preventing future outages” as part of upcoming FAA reauthorization legislation. 

“The number one priority is safety,” she said. “The public needs a resilient air transportation system.”

Rep. Garret Graves, R-La., who is likely to chair the House Transportation and Infrastructure Subcommittee on Aviation, said it’s clear that “significant improvements across the aviation system are needed.”

The outage comes just days after Cantwell announced she will also investigate Southwest Airlines’ mass cancellations over the holiday season.

“Every person is stranded east to west — business travelers, tourists, and those visiting friends and family. Air travel logistics are hard enough — we do not need our government making it worse,” Graves said in a statement Wednesday. “We will aggressively pursue accountability and craft reforms that focus on enhancing the passenger experience.”

Transportation Secretary Pete Buttigieg told CNN he was pleased by the interest Congress has expressed in the FAA breakdown.

“I welcome the attention from Congress,” he said, “especially because we’re coming up on the period when the FAA reauthorization, the five-year bill that provides funding and direction for the FAA, is coming before Congress.”