Just shy of two hours after the problems began, the Federal Aviation Administration lifted the ground stop order.

United said it was recovering from a “network connectivity issue” and restoring regular flight operations. The airline said that it would have a waiver available on its website for customers that are able to change their flight plans.

It is the second time in two months that the carrier has been hit by major technical issues.

The Chicago company had halted all takeoffs in the U.S. on June 2 due to what the airline described as computer automation issues.

The Federal Aviation Administration used the same language in its notice about the outage Wednesday.

United suffered a series of computer problems in 2012 after switching to a passenger information computer system previously used by merger partner Continental Airlines.

In each case, hundreds of flights were delayed. A number of high-paying business travelers defected to other airlines and revenue dropped.

“We don’t know everything behind this morning’s issues yet, but today’s incident underscores the sense that something is very wrong at United,” said Gary Leff, co-founder of frequent-flier website MilePoint.

Shares of United Continental Holdings Inc. slid 2 percent to $53.20 in morning trading.

Michelle Chapman in New York, Matt Small in San Francisco, and Joan Lowy in Washington contributed to this story.

UPDATED 10:06 AM: PORTLAND — Passengers at the Portland Jetport experienced longer wait times Wednesday morning because the FAA grounded United airline flights.

The airline simply said, “We experienced a network connectivity issue this morning. We are working to resolve this and apologize to our customers for any inconvenience.” The FAA cited “automation issues” as the reason for its grounding.

Around 9:30 a.m., the FAA said in an advisory that the ground stop is for United Airline “mainline” only flights. It goes on to say that sub carriers for United “have been released from the ground stop.”

Portland Jetport tweeted that their United operation was affected but systems were returning to normal after 9:30 a.m.

Our @united systems are returning to normal operations. United is working to accommodate all impacted customers. Current wait time 10min

— Portland Jetport (@portlandjetport) July 8, 2015

We experienced a network connectivity issue. We are working to resolve and apologize for any inconvenience.

— United (@united) July 8, 2015

Our @united operation was impacted by this mornings system outage. Agents are currently assisting pax. Wait <5min. pic.twitter.com/vae2FZIk9B

— Portland Jetport (@portlandjetport) July 8, 2015

All @united customers at PWM have been assisted from this mornings system failure. Flights to Newark and Washington will board shortly.

— Portland Jetport (@portlandjetport) July 8, 2015