WASHINGTON -- The NFL players' union filed a collusion claim against the league's owners, another move in the back-and-forth between the sides as they near the expiration of their labor contract.

The union originally had until December -- 90 days after the start of the season -- to accuse teams of conspiring to restrict players' salaries last offseason, but the league agreed to extend that deadline.

"They have filed that claim. They filed it probably a week ago. There has been no activity at this point. But it's something that was not unexpected," the league's lead labor negotiator, Jeff Pash, said Tuesday, when owners met in Atlanta. "It's just another piece of litigation that we have to work our way through. So we will do that."

The case is before Stephen Burbank, the same special master who is considering a complaint about the league's TV contracts, which the union says were set up to guarantee the NFL money even if there were a lockout this year.

Union spokesman George Atallah said Tuesday he could not comment on the collusion case. Pash said no date has been scheduled for a hearing.

"It is something they were committed to doing. Their attorneys told us that they didn't see any reason to delay it any further," Pash said. "Our reaction was, 'That's fine. If you feel you have a claim and want to file, go ahead and file."

Collusion has been an issue in Major League Baseball, and as recently as September, for example, players and owners in that sport settled allegations of possible collusion against free agents after the 2008 and 2009 seasons. As part of the agreement -- with no admission of guilt by the teams -- some of baseball's free-agency rules were changed.

In the 1980s, arbitrators found baseball teams acted in concert against free agents following the 1985, 1986 and 1987 seasons, and the sides agreed to a $280 million settlement -- which took until 2005 to be completely distributed to the players following claims hearings.

NFL owners and players are trying to negotiate a collective bargaining agreement to replace the one that expires in March. Among the key issues are how league revenues will be split by the sides moving forward; the possible move to an 18-game regular season; a rookie wage scale; and pensions for former players.