The National Football League will require all players to "stand and show respect for the flag" during the national anthem before games — or else stay off the field until the song ends.

The new policy was adopted Wednesday, the league's commissioner, Roger Goodell, said in a statement. Players who refuse to stand for the anthem "may stay in the locker room or in a similar location off the field until after the Anthem has been performed," Goodell said.

Goodell maintained that the wave of players kneeling in protest during the anthem, sparked in 2016 by San Francisco 49ers quarterback Colin Kaepernick, created "awareness and action around issues of social justice that must be addressed."

However, Goodell added that "It was unfortunate that on-field protests created a false perception among many that thousands of NFL players were unpatriotic. This is not and was never the case."

The protests became a political lightning rod as politicians across the country weighed in on the players' actions. President Donald Trump repeatedly criticized the players who knelt, at times calling for the NFL to be punished.

Trump tweet

If players break the new rules, their teams will be fined, Goodell's statement said. No specific dollar amount was provided in the statement, although the commissioner added that he "will impose appropriate discipline" on those who do not stand for the anthem.

Kaepernick became a free agent in 2017 and went unsigned all last season. He is suing NFL teams, accusing them of colluding against him to keep him off the field.

The league's union, the NFL Players Association, accused the new policy of contradicting past statements from NFL leadership.

"The NFL chose to not consult the union in the development of this new 'policy,'" the union said in a statement. "NFL players have shown their patriotism through their social activism, their community service, in support of our military and law enforcement and yes, through their protests to raise awareness about the issues they care about."

The union also vowed to challenge any aspect of the new rules that are "inconsistent with the collective bargaining agreement."

The American Civil Liberties Union offered its own criticism for the NFL's policy change in a Twitter statement.

ACLU tweet