UPDATE: United Airlines lifted the ground stop around 6 p.m.
United Airlines announced that a ground stop is in place for U.S. flights on Sunday evening.
The announcement was made around 5 p.m. via Twitter. The company says they're experiencing an IT issue.
19 flights in Las Vegas are affected by the ground stop. No word yet on when it will be lifted.
Many passengers were upset, though a few Twitter users had a sense of humor about the incident.
— andrew_ (@nexus9988) January 23, 2017
— boilergrad (@Boilers32) January 23, 2017