The NFL Players Association has filed a collusion complaint against the league, charging teams with improperly conspiring to restrict players’ salaries during the sport’s season without a salary cap in 2010.

The union announced the filing Wednesday, one day after an arbitrator dismissed a case in which the Washington Redskins and Dallas Cowboys contested salary cap reductions imposed on them by the league — with the union’s assent — for the way the teams structured players’ contracts during the uncapped year.

The union’s complaint alleges that the league had a secret salary cap of $123 million per team during the uncapped year, according to the NFLPA’s announcement.

The case was filed, according to the union, in the federal court in Minnesota that oversaw the sport’s previous collective bargaining agreement. That labor deal was in effect during the uncapped year in 2010.

“When the rules are broken in a way that hurts the game, we have an obligation to act,” DeMaurice Smith, the union’s executive director, said in a written statement. “We cannot stand by when we now know that the owners conspired to collude.”

The league denied the accusations.

“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.”

According to the NFL, the union also is barred from making its collusion claim.

“The filing of these claims is prohibited by the Collective Bargaining Agreement and separately by an agreement signed by the players’ attorneys last August,” Aiello said in a written statement. “The claims have absolutely no merit, and we fully expect them to be dismissed. On multiple occasions, the players and their representatives specifically dismissed all claims, known or unknown, whether pending or not, regarding alleged violations of the 2006 CBA and the related settlement agreement. We continue to look forward to focusing on the future of the game rather than grievances of a prior era that have already been resolved.”

The league and union settled legal claims as part of their labor deal last summer that followed a 4 1 / 2-month lockout of the players and a courtroom confrontation.

The two sides filed a “stipulation of dismissal” of last year’s antitrust lawsuit by the players in federal court in Minnesota in August that said “the parties stipulate to the dismissal with prejudice of all claims, known and unknown, whether pending or not, regarding the Stipulation and Settlement Agreement…”

That dismissal agreement specifically mentions a case brought by the players involving the league’s television contracts and a previous collusion claim by the players.

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.

“Our union recently learned that there was a secret salary cap agreement in an uncapped year,” veteran 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.”

In its 20-page complaint, the union estimates that actual damages to the players from the alleged collusion could be $1 billion or substantially more, resulting in total potential damages — once multiplied under CBA provisions — of more than $3 billion. But Jeffrey Kessler, an attorney for the union, said during an afternoon conference call with reporters that the union had not done its final damage estimates.

Kessler said it was coincidental that the collusion case was filed on the day after the dismissal of the arbitration case involving the Redskins and Cowboys. The collusion case is designed to benefit the players, not the Redskins and Cowboys, he said.

“This lawsuit is not about the 2012 penalties,” Kessler said. “It’s about the collusion in 2010.”

Kessler and a union spokesman said on the conference call that the union agreed to the salary cap reductions for the Redskins and Cowboys only because the league made a take-it-or-leave-it offer that, if rejected by the union, would have resulted in the salary cap for all teams being set lower. The union didn’t suspect then, Kessler said, that the teams had engaged in collusion in 2010.

According to the union, the federal court in Minnesota rejected last year’s agreement by which the league and union would have dismissed all legal claims, pending or not, and instead dismissed only those claims that existed at the time. Kessler said the union believes it also is within the 90-day limit set in the 2006 labor deal for filing a collusion claim once a violation is known or reasonably should have been known. The union called its case strong.

“I think the amount of evidence frankly is extraordinary so far, without discovery,” Kessler said.

In its collusion filing, the union says the league estimated that the Redskins spent $225.8 million on players in 2010, or nearly $103 million above the secret salary cap alleged by the union, and the Cowboys spent $175.9 million.

Under the CBA, teams are prohibited from conspiring to restrict players’ salaries.

The collusion case charges the league with violating the agreement that first put the sport’s salary cap and free agency system in place in the early 1990s. The system resulted from a settlement of antitrust litigation and put the sport’s labor deal under the jurisdiction of the Minnesota court.

Such federal court oversight was removed in last year’s 10-year CBA between the league and union, but the alleged collusion took place during the previous labor deal, when court oversight was in effect.

Stephen Burbank, a University of Pennsylvania law professor who is the sport’s system arbitrator, on Tuesday dismissed the case in which the Redskins and Cowboys were contesting their salary cap cuts imposed by the league in March.

Burbank ruled that, because the league and union agreed to the reductions, the cuts amounted to a proper amending of the CBA and the two teams could not bring such a case.

The Redskins’ salary cap was reduced by $36 million over two seasons. The Cowboys’ cap was cut by $10 million over two seasons. The teams voted, 29-2, in late March to affirm the reductions. The Redskins and Cowboys voted against that resolution, and the Tampa Bay Buccaneers abstained.

According to people familiar with the case, the league found the two teams technically violated no salary cap rules but attempted to gain an unfair competitive advantage.

The Redskins and Cowboys reworked contracts to pay money to players during the uncapped year that otherwise would have been paid in subsequent years when a salary cap presumably would be back in place, according to those people familiar with the case, thus clearing cap space for future seasons.

The $46 million in salary cap reductions was redistributed to 28 of the other 30 NFL teams. The league found the New Orleans Saints and Oakland Raiders to have used similar tactics but to a lesser degree. They received no salary cap reductions but did not benefit from the $46 million redistribution.

The Redskins and Cowboys denied wrongdoing and pointed out the contracts were approved by the league at the time. They filed their arbitration case against both the league and the union.

A person familiar with the union’s view of the salary cap cuts previously said the NFLPA believed the two teams did nothing wrong but agreed to the cuts to avoid the salary cap being set lower for all teams.

This season’s salary cap is $120.6 million per team. The 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.

The union contends the NFL and the owners “furthered their concealment” by approving contracts 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.”

The 2010 season was played without a salary cap under a provision in the previous labor deal. The salary cap went back into effect last year with the ratification of the current CBA.

One person with knowledge of the case said Wednesday he believes the Redskins and Cowboys likely are done contesting their cap reductions after Tuesday’s dismissal of their arbitration case. The teams issued a joint written statement Tuesday saying they would abide by the dismissal.

The collusion case is filed at a time when the league and union have been at odds over a variety of issues, including the league’s suspensions of four players in the bounty case involving the New Orleans Saints and, most recently, the owners’ vote Tuesday to require players to wear knee and thigh pads during games beginning in the 2013 season.

NFL Commissioner Roger Goodell said Tuesday he accepts the contentiousness with the union as part of normal business operations.

“We continue to address the issues,” Goodell said at a news conference in Atlanta at the completion of the owners’ one-day meeting there Tuesday. “We don’t always agree but we seek resolutions. Sometimes we’ll reach a consensus and sometimes we won’t.”