Just a few months after reaching an agreement on a new collective bargaining agreement with the NFL, the NFL Players Association has filed a complaint in federal court accusing to league of colluding to impose a secret salary cap during the uncapped 2010 season.

The motion claims the move cost the players at least $1 billion. The claim was filed in U.S. District Court in Minnesota, which oversees the Reggie White settlement covering NFL labor matters.

Adding to the tension between the two sides, during this off-season alone, the union has already filed grievances in the Saints bounties case and for drug-related suspensions for two Denver Broncos.

“The reality is that is part of operating in a pretty complex world,” NFL commissioner Roger Goodell said when asked about the difficulty of negotiation with the NFLPA. “You have to be open about the initiatives you want to undertake. You don't expect all parties to agree at any point in time, but you have to drive toward solutions. At some point, you have to make some decisions about what is best for the game.”

The complaint claims a "conspiracy" to set a $123 million salary cap for the 2010 season, when owners did not have the legal authority to do so. The Dallas Cowboys and Washington Redskins have had their future salary caps lowered for going over the limit in 2010.

Washington $36 million and Dallas $10 million.

The league says the union has no grounds for the action and is prohibited from filing it by the collective bargaining agreement.