United Airlines passengers at Chicago's O'Hare International Airport took to social media Tuesday morning to complain of flight delays because of an apparent computer glitch involving boarding passes.
In an emailed statement just after 1:30 p.m. the airline said the system had been restored and crews were working to "get our customers to their destinations as soon as possible."
The airline said "intermittent issues" with its passenger service system caused the delays.
"We are experiencing issues with our passenger service computer system," United said earlier in the day. "We are working to resolve this as quickly as possible and apologize to our customers for any inconvenience."
It's not clear what caused the glitch.
Customers wrote on Twitter that the outage spurred long lines and poor communication from customer service. Others said they were told boarding passes couldn't be printed.
According to reports, the computer issues occurred at other airports too, with complaints coming from fliers at Dulles and Los Angeles airports.