The NFL Players Association filed a grievance on Tuesday against the league's new national anthem policy.
NFL commissioner Roger Goodell announced in May that the league would enact a national anthem policy for the 2018 season that requires players and league personnel to either stand for the anthem or remain in the locker room.
The policy subjects teams to a fine if a player or any other personnel do not show respect for the anthem.
"Our union filed its non-injury grievance today on behalf of all players challenging the NFL's recently imposed anthem policy," the NFLPA said in a statement. "The union's claim is that this new policy, imposed by the NFL's governing body without consultation with the NFLPA, is inconsistent with the collective bargaining agreement and infringes on player rights.
"In advance of our filing today, we proposed to the NFL to begin confidential discussions with the NFLPA Executive Committee to find a solution to this issue instead of immediately proceeding with litigation. The NFL has agreed to proceed with those discussions and we look forward to starting them soon."
Under Article 43 of the collective bargaining agreement, franchises have the right to implement "reasonable club rules."
The NFL will have 10 days to respond in writing to the accusations in the grievance.
NFLPA president Eric Winston told Sirius XM NFL Radio on Tuesday that he is hopeful the talks will lead to a compromise between the sides.
"Players are hoping to get together and come together with ownership and find a solution," said Winston. "I think that's what's best for the game. I think when we've done that, when we've had solutions that have come from both sides, that's been good."
The anthem issue has been a divisive one, with some feeling that players who don't stand for the song are being disrespectful to, among others, the U.S. military. Others feel it is the players' right to protest perceived social injustice peacefully.
Former San Francisco 49ers quarterback Colin Kaepernick started the movement in 2016 to kneel during the national anthem as a protest to denounce police brutality against African-Americans, social injustice and racial inequality.
Kaepernick and former 49ers safety Eric Reid have both filed collusion cases against the league after failing to land jobs as free agents.
The anthem topic became a central issue for the NFL after President Donald Trump criticized the movement during a speech last September, stating players should be fired for not standing.