MINNEAPOLIS — A $4 billion lawsuit from the players union accusing NFL team owners of setting a secret salary cap in 2010 was kept alive by a federal appeals court Friday as the sniping between the two sides persists long after the end of the lockout.

The 8th U.S. Circuit Court of Appeals in St. Louis partially reversed a federal judge’s order that had rejected the union’s collusion claim, sending the case back to U.S. District Judge David Doty for further proceedings.

The three-judge appeals court panel that heard oral arguments in January disagreed with Doty on one of the union’s two arguments for pursuing damages despite the 2011 collective bargaining agreement that was supposed to relinquish the union’s right to sue for alleged breaches of the old CBA.

The NFL called the appeals court decision “entirely procedural in nature” and said it’s “far from validating” the claims of the NFL Players Association.

“The Court specifically highlighted the heavy burden that the NFLPA faces in establishing this claim, and we remain highly confident that the claim will be dismissed yet again,” the NFL said in a written statement.

The league, however, could be forced to make public otherwise-confidential financial and strategic information in court, which the union has pushed for all along.

“We are pleased that the Eighth Circuit ruled that players have the opportunity to proceed with their claims,” the NFLPA said. “Through discovery and a hearing, we can understand how collusion took place. We have notified the NFL of its obligations to preserve all relevant documents and communications.”

The collusion claim seeking at least $4 billion in relief for the players was originally filed in May 2012, less than a year after the new CBA was implemented following a five-month lockout. The final year of the prior CBA was supposed to be “uncapped,” but the union cited public references by New York Giants owner John Mara and NFL Commissioner Roger Goodell as evidence that a salary cap existed and claimed a loss of $1 billion in cumulative compensation.