NEW YORK (Reuters) – President Donald Trump on Friday lobbed barbs at protesters who kneel during the national anthem, after NFL quarterback Drew Brees apologized for remarks he made about the practice.

Brees said this week that he would “never agree with anybody disrespecting the flag,” referring to the possibility of players kneeling during the “Star-Spangled Banner” in the upcoming NFL season. Brees apologized on Thursday, saying his words “lacked awareness and any type of compassion or empathy.”

The kneeling pose has become a symbol of the fight for racial justice in the United States.

Trump tweeted on Friday that Brees “should not have taken back his original stance.”

“We should be standing up straight and tall, ideally with a salute, or a hand on heart,” Trump wrote. “There are other things you can protest, but not our Great American Flag – NO KNEELING!”

The kneeling pose has been seen at protests against police brutality in cities across the country in the wake of the death of George Floyd, an unarmed black man, while in police custody in Minneapolis.

NFL quarterback Colin Kaepernick popularized the move in 2016 while he was on the San Francisco 49ers roster, appearing on NFL sidelines first sitting, and later kneeling, during the customary pre-game airing of the U.S. national anthem.

Trump was an early critic of the protest, and in 2017 Vice President Mike Pence walked out of an NFL game between the 49ers and the Indianapolis Colts when some of the players knelt on the sidelines during the anthem.