United said it is due to a weight and balance computer system issue.

United Airlines has grounded flights nationwide on Wednesday night due to an issue with its weight and balance computer system, according to the airline.

"Due to a technology issue, we are holding United mainline flights at their departure airports," United said in a statement. "We expect additional flight delays this evening as we work through this issue. Safety is our top priority, and we'll work with our customers to get them to their destinations."

The airline confirmed in a statement to ABC News that it is not a cyberattack.

The ground stop does not affect United Express flights, and any flight that is already in the air will continue to its destination, according to the airline.

Multiple FAA notices have stated that the airline has requested ground stops at major hubs, including Newark, San Francisco, Chicago, Denver and Houston.