American Airlines flights were cleared to fly by regulators early Tuesday after a brief grounding due to a systemwide technical issue.

Just before 7 a.m. Eastern time, the Federal Aviation Administration ordered all American Airlines flights grounded in the U.S. at the airline’s request. American had reported a technical issue affecting its entire system with millions traveling for the holiday.

In social media replies to frustrated travelers, the airline said: “Our team is currently working to rectify this. Your continued patience is appreciated.”

The company has not issued a press release explaining the issue and an email was not immediately returned.

A post on the Federal Aviation Administration’s website acknowledged the airline’s request for a “nationwide groundstop” for all American Airlines planes and their subsidiary airlines.

The grounding occurred with millions of travelers expected to fly over the next 10 days.

The Transportation Security Administration expects to screen 40 million passengers over the holidays and through January 2.