The first lady and Jill Biden, wife of the vice president, were at the Homestead-Miami Speedway as part of their Joining Forces initiative to support military families. They were promoting legislation signed by President Obama today to boost veteran employment.
On video of the moment being widely circulated Monday, the sounds of booing can be heard just as Obama is announced to the crowd.
Officials don't doubt that some fans may have indeed booed but say the incident is being overblown.
"It didn't strike our attention at all until we started seeing clips and some overinflated blogs," David Higdon, a NASCAR spokesman, said in an interview.
He said that often before races when dignitaries are announced, they get "rounds of applause and sometimes a smattering of boos."
"It could be anyone from the first lady to a notable athlete or celebrity. There was nothing abnormal," he said. "We're disappointed that it got overblown ... but that's the political climate that we're in."
Along with Obama and Biden, representatives from companies that have committed to hiring veterans and their spouses volunteered at a barbecue lunch before Sunday's Ford 400. Some of the drivers gave Obama "a little taste of NASCAR," showing off the cars and technology before the race, Higdon said.
"The NASCAR community and the vast majority of those attending our race Sunday welcomed the first lady and Dr. Jill Biden and the military families in attendance," Marcus Jadotte, NASCAR vice president of public affairs, said in a statement.
The first lady's office said Obama and Biden "enjoyed their visit to the speedway and are looking forward to working across the country to honor America’s veterans and military families."
"As she has always said, she will proudly stand with anyone making a major commitment to serve and honor our military community and yesterday, NASCAR did just that," Kristina Schake, the first lady's communications director, said.