US President Donald Trump has called for the National Football League (NFL) to be stripped of tax advantages.
In a tweet, he complained the league had received massive tax breaks, while some of its players had been disrespecting the national anthem.
The teams pay tax, but have often received public support to build stadiums.
The NFL league office, which oversees rules, referees and the college draft, gave up its tax-exempt status in 2015.
Dozens of players have been kneeling down during the pre-match national anthem, instead of standing, in anger at comments made by the president.