The NFL will fine teams if their players fail to stand during the national anthem after a vote by league owners on Wednesday.
Commissioner Roger Goodell announced the agreement on the contentious issue, which spiraled into a national debate last year over the right of players to protest versus respect for the American flag and its symbolism.
Goodell added players who don't wish to stand for the anthem don't have to be on the field for its playing, the New York Times reported.
"This season, all league and team personnel shall stand and show respect for the flag and the anthem," Goodell said in a statement. "Personnel who choose not to stand for the anthem may stay in the locker room until after the anthem has been performed."
"We believe today’s decision will keep our focus on the game and the extraordinary athletes who play it—and on our fans who enjoy it."
The policy states, "a club will be fined by the league if its personnel are on the field and do not stand and show respect for the flag and the anthem." The Times noted it didn't make clear whether such a gesture as a raised fist would be considered inappropriate.
Former San Francisco 49ers quarterback Colin Kaepernick began the protest when he started kneeling during the national anthem in 2016. He did it as a protest against police brutality and racial injustice. Some other players followed suit, although the majority didn't.
The NFL Players' Association said the NFL did not consult with the union over the new policy, defending players who have shown "patriotism" through such protests.
— NFLPA (@NFLPA) May 23, 2018
It added, "Our union will review the new 'policy' and challenge any aspect of it that is inconsistent with the collective bargaining agreement."
Kaepernick received praise in some circles for using his platform to draw attention to important social issues, while critics hit him for disrespecting the flag, the police and the military. The NFL saw a drop in attendance last season, which may have been tied to displeasure with players kneeling or sitting down during the anthem.
Kaepernick, who hasn't played since 2016, has said he's been blackballed since he started the protests. He filed a grievance last year against the NFL, claiming the league's owners colluded to prevent him from being signed after becoming a free agent last year.
The issue has had strong political implications under the Trump administration.
President Donald Trump said players who didn't stand for the national anthem should be fired, saying at one point they should "get that son of a bitch off the field" if he does. Vice President Mike Pence and Second Lady Karen Pence left an Indianapolis Colts game early in October in protest of some 49ers players who knelt during the national anthem.