Southwest Airlines on Sunday said it is investigating an incident in which a pilot allegedly said “Let’s Go Brandon” – a phrase meant to insult U.S. President Joe Biden – over the intercom during a flight.

The incident reportedly took place Friday on a Southwest flight from Houston to Albuquerque.

“Let’s Go, Brandon” has taken on life as an anti-Biden meme.

The phrase originated at a NASCAR race in early October during a live TV interview with winner Brandon Brown. In the background, the largely conservative crowd could be heard chanting “F–k Joe Biden!” The interviewer reported that the crowd was shouting “Let’s Go Brandon,” and the phrase has been a euphemism ever since.