The NFL announced a new national anthem policy on Wednesday, requiring all team and league personnel on the field "to stand and show respect for the flag and the anthem."
That policy, which stemmed from many players kneeling in protest last season for social justice reasons, was immediately challenged by the NFLPA, which issued a statement saying it would "review the new 'policy' and challenge any aspect of it that is inconsistent with the collective bargaining agreement."
In its statement, the NFLPA said the NFL "chose to not consult the union" while developing the new policy, and said that the vote by NFL club CEOs "contradicts the statements made to our player leadership by Commissioner Roger Goodell and the Chairman of the NFL's Management Council John Mara about the principles, values, and patriotism of our League."
In the NFL's new anthem policy, it notes that personnel who choose not to stand for the anthem may stay in the locker room or a similar location off the field until its conclusion.
The commissioner will "impose appropriate discipline" for those on the field "who do not stand and show respect for the flag and the Anthem."
Jets owner Christopher Johnson said in March that trying to force a policy on the players wasn't something he thought should happen.
"I can't speak to how other people run their teams, he said, "but I just think that trying to forcibly get the players to shut up is a fantastically bad idea."
The kneeling began as a commentary on social justice by Colin Kaepernick during the 2016 season, and increased last season after president Donald Trump said players who kneel should lose their jobs and referred to them as sons of bitches.
"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, out, he's fired. He's fired," Trump said.
Several Giants knelt during the anthem at different points last season, while Jets players locked arms.