United States President Donald Trump went after two of America’s most popular sport leagues and triggered a backlash from several athletes on Saturday. Trump went on a Twitter tirade and said the National Football League should fire players who protest during the national anthem, and withdrew a White House invitation to NBA champions Golden State Warriors because of their star player Stephen Curry’s public opposition to him.

On Friday, Trump, at a public rally used an expletive to describe players who kneel or sit during the anthem, to protest police brutality against black Americans and other forms of social injustice, The New York Times reported. Trump was referring to a controversial string of protests over racism started last year by NFL player Colin Kaepernick.

“Wouldn’t you love to see one of these NFL owners, when somebody disrespects our flag, to say, ‘Get that son of a bitch off the field right now... he is fired,” Trump told a cheering crowd at the rally.

The NFL, and some of its current and former players decried the president’s remarks. NFL commissioner Roger Goodell released a statement saying “divisive comments like these demonstrate an unfortunate lack of respect”, the BBC reported. Executive director of the NFL Players Association, DeMaurice Smith, said the union “will never back down when it comes to protecting the constitutional rights of our players as citizens as well as their safety as men who compete in a game that exposes them to great risks”.

On Saturday night, Oakland Athletics’ Bruce Maxwell kneeled in protest during the national anthem, while the CEO of the San Francisco 49ers – Kaepernick’s former team – said he would continue to support his players. “The callous and offensive comments made by the President are contradictory to what this great country stands for,” the BBC quoted Jed York as saying.

There were a stream of strong reactions from other NFL players, including Minnesota Vikings running back Bishop Sankey and Kansas City Chiefs’ Chris Conley.

But Trump was unmoved. He wrote on Twitter: “If a player wants the privilege of making millions of dollars in the NFL or other leagues, he or she should not be allowed to disrespect our Great American Flag (or Country) and should stand for the National Anthem. If not, YOU’RE FIRED. Find something else to do!”

On Saturday, Trump also withdrew a White House invitation to basketball champions the Golden State Warriors, after one player, Stephen Curry, said he did not want to attend, The New York Times reported. “Going to the White House is considered a great honor for a championship team,” Trump tweeted afterwards. “Stephen Curry is hesitating, therefore invitation is withdrawn!”

In response, triple NBA champion LeBron James, called the President a “bum”.

Trump’s latest comments come at a time when there is already fiery debate over race, social justice and athlete activism in the country.