The union alleged owners used a covert cap to hold down salaries in the uncapped 2010 season.
The NFL Players Association has appealed a judge's recent rejection of the union's claim that the league colluded to set a secret salary cap in 2010.
The NFLPA filed the appeal on Wednesday to the 8th U.S. Circuit Court of Appeals in St. Louis.
U.S. District Judge David Doty ruled on Dec. 31 in Minneapolis that the union could not reopen the Reggie White lawsuit that guided league labor matters from 1993 until the new collective bargaining agreement in 2011.
The union alleged owners used a covert cap to hold down salaries in the uncapped 2010 season. The players sought at least $4 billion in damages.
In the current CBA, though, all pending claims related to the White case were thrown out, and the players relinquished their right to sue.