“There was no collusion. There was no agreement. These claims are totally unfounded,” says Greg Aiello, the NFL’s senior vice president of communications. (Luis Alvarez/AP)

The NFL Players Association sued the league for collusion Wednesday, charging that team owners agreed to abide by a secret salary limit of $123 million per franchise that improperly restricted player salaries during the 2010 season, when pro football had no salary cap.

The union estimates in its complaint that owners could owe players $1 billion or more in damages for conspiring to violate the agreement that established the NFL’s salary cap and free agency system in 1993. The suit was filed in the Minnesota federal court that oversaw the sport’s collective bargaining agreement until last year, when a new labor pact removed that power from that court.

“Our union recently learned that there was a secret salary cap agreement in an uncapped year,” cornerback Domonique Foxworth, the union president, said in a written statement. “The complaint today is our effort to fulfill our duty to every NFL player. They deserve to know, above all, the facts and the truth about this conspiracy.”

The NFL imposed severe penalties on the Washington Redskins and Dallas Cowboys for reworking some player salaries into 2010 contracts. The NFL, saying that was an effort to free up space in subsequent capped years and gain a competitive advantage, stripped the Redskins of $36 million in cap space over two years and cut the Cowboys’ cap space by $10 million over the same time.

In its complaint, the union says the league estimated that the Redskins spent $225.8 million on players in 2010, or nearly $103 million above the alleged secret salary cap, and the Cowboys spent $175.9 million. On Tuesday, an arbitrator turned down a bid by the two teams to overturn the penalty.

The two teams’ cap space was redistributed to 28 other teams in an agreement signed by the union. (The league found the New Orleans Saints and Oakland Raiders had used similar tactics but to a lesser degree, so they received no extra cap space.)

But NFLPA attorney Jeffrey Kessler said the union was not aware of the alleged collusion when it made the redistribution deal and did so only because the league made a take-it-or-leave-it offer that, if rejected by the union, would have cut the salary cap for all 32 teams.

The NFL denied the lawsuit’s accusations and said the union agreed in the new CBA to dismiss all claims that arose out of the previous labor contract.

“There was no collusion,” Greg Aiello, the NFL’s senior vice president of communications, said in a written statement. “There was no agreement. These claims are totally unfounded.”

The union, however, said that the federal court in Minnesota rejected last year’s agreement to dismiss all legal claims, pending or not, and instead dismissed only those that existed at the time.

The lawsuit comes at a tense time between the NFL and its players’ union, which have been at odds over a variety of issues. They include the league’s suspensions of four players in the New Orleans Saints bounty case; league efforts to crack down on blows to players’ heads and most recently, the owners’ vote Tuesday to require players to wear knee and thigh pads during games beginning in 2013.

The union’s collusion claim cites public comments by New York Giants co-owner John Mara, the chairman of the owners’ bargaining committee, made in relation to the salary cap case involving the Redskins and Cowboys. Mara said the actions by the Redskins and Cowboys violated the spirit of the salary cap.

The union contends the NFL and the owners “furthered their concealment” by approving player contracts worked out by the Redskins, Cowboys, Saints and Raiders. The union maintains the league and owners failed to disclose to the players or the NFLPA “that the true reason for the then-proposed reallocation was to penalize the Redskins, Cowboys, Raiders, and Saints for not fully abiding by the collusive agreement.”

This season’s salary cap is $120.6 million per team. A person familiar with the union’s views previously said the cap would have been set around $115 million per team if the union had not agreed to the reductions for the Redskins and Cowboys, a figure that would have reduced money available to players throughout the league.