The NFL Players Association said today that it had filed a grievance against the league for unilaterally changing its policy on the national anthem, the latest salvo in the nearly two-year controversy over whether players should be allowed to kneel during the anthem.

In a statement, the union said the league had changed the policy without consulting the Players Association, something that “is inconsistent with the collective bargaining agreement and infringes on player rights.”

The NFL did not comment today.

At a meeting in late May, the 32 NFL owners voted to overhaul their protocol for what players must do during the anthem. In the past, players were required to be on the sideline during the anthem, but they were not required to stand. That policy dated back to 2009, when the NFL signed a marketing deal with the U.S. military.

Under the new policy, players can no longer kneel during the national anthem without leaving themselves open to punishment. Also their teams could face possible financial penalties. At the same time, players are not required to be on the sideline during the playing of the anthem. They can remain in their locker room during the pregame ceremony.

The union immediately objected to the revised policy, saying it was not consulted.

The players have long contended they are not protesting the flag or the anthem, but trying to raise awareness to important issues.

The union said it offered to begin confidential discussions with the league before proceeding to potentially contentious and time-consuming litigation. The league agreed, the union said.

If talks fail, the union will begin discovery and ultimately can present its case to an independent arbitrator. It is unclear what remedies the union is seeking.

The controversy dates back to August 2016 when Colin Kaepernick, then a quarterback with the San Francisco 49ers, initially sat and then knelt during the playing of “The Star-Spangled Banner” during preseason games to draw attention to police brutality against African-Americans and other instances of social injustice. He continued the demonstration into the regular season, with other players on the 49ers and on other teams later joining him.

Kaepernick became a free agent after the season, and his inability to find a new club willing to sign him led to accusations that the owners were punishing him because of his political views. Kaepernick later filed a grievance against the NFL and the owners, accusing them of colluding to keep him out of the league.

Last September, the issue exploded into a national controversy when President Donald Trump said the owners should fire any players who did not stand for the anthem. In a meeting held several weeks after the president first attacked the league, the owners talked openly about the threat to their businesses, and pleaded with the players to stop protesting.

Soon after, the NFL and a coalition of players announced a plan to donate millions of dollars to groups addressing social injustice.

After the season, the owners began discussing how to tweak their anthem policy to appease fans who sided with the president, while leaving room for the players to express themselves.

The new policy, though, makes clear that players could be fined if they “do not stand and show respect for the flag and the anthem.”

“We want people to be respectful of the national anthem,” Commissioner Roger Goodell said at the meeting in May when the policy was changed.

With the start of the season less than two months away, it is unclear how the union will be able to alter the policy.

There are areas of the policy, though, that could be clarified, including what fines might be assessed.