Southwest Airlines announced an internal investigation after a pilot was reported to have signed off a message to passengers by saying: “Let’s go Brandon.”

The apparent non-sequitur is in fact a rightwing meme, based on a NBC sportscaster’s apparent mishearing of a chant of “Fuck Joe Biden” by a crowd at a Nascar circuit in Alabama at the start of October.

On a Southwest flight from Houston, Texas to Albuquerque, New Mexico on Friday morning, an Associated Press reporter heard the pilot end a message over the public address system with the phrase, prompting gasps from some passengers.

The reporter, Colleen Long, said she tried to ask the pilot about his comment but was “almost removed from [the] plane”.

As discussion of the incident proliferated online, Southwest said in a statement it “takes pride in providing a welcoming, comfortable, safe and respectful environment for the millions of customers who fly with us each year.

“Southwest does not condone employees sharing their personal political opinions while on the job, serving our customers. And one employee’s individual perspective should not be interpreted as the viewpoint of Southwest and its collective 54,000 employees.

“Southwest is conducting an internal investigation into the recently reported event.”

Predictably popular among supporters of Donald Trump, the man Joe Biden soundly beat for the White House last year, “Let’s go Brandon” swiftly reached the halls of Congress.

Among uses by House Republicans, the Florida representative Bill Posey ended a floor speech with a fist pump and the phrase while Jeff Duncan, from South Carolina, wore a “Let’s Go Brandon” mask at the Capitol.

In the Senate, Ted Cruz of Texas posed with a sign at a World Series game while the press secretary for Mitch McConnell of Kentucky, the Senate minority leader, retweeted a photo of the phrase on a construction sign in Virginia.

Trump’s fundraising committee now sells a $45 T-shirt featuring “Let’s go Brandon” above an American flag. One message to supporters read: “#FJB or LET’S GO BRANDON? Either way, President Trump wants YOU to have our ICONIC new shirt.”

Southwest said it would “address the situation directly with any employee involved while continuing to remind all employees that public expression of personal opinions while on duty is unacceptable.

“Southwest does not tolerate any behavior that encourages divisiveness as it does not reflect the Southwest hospitality and inclusiveness for which we are known and strive to provide each day on every flight.”