LOS ANGELES - The NFL Players Association has filed a federal lawsuit seeking to overturn a ruling which upheld the suspension of Vikings running back Adrian Peterson.
NFL running back Adrian Peterson addresses the media on November 4, 2014 in Conroe, Texas
Peterson was suspended indefinitely -- and at least through April 15 -- after pleading no contest in November to a misdemeanor charge for whipping his son with a tree branch.
NFL-appointed arbitrator Harold Henderson on Friday upheld the sanction, saying the ruling was neither unfair nor inconsistent.
The NFLPA argued in its petition Monday that Henderson's decision "is contrary to the essence of the NFL-NFLPA Collective Bargaining Agreement; it defies fundamental principles of notice, fairness, and consistency; and it was rendered by an evidently partial arbitrator who exceeded the scope of his authority."
Peterson received probation and a $4,000 fine over the incident, and was required by a Texas judge to perform 80 hours of community service.
NFL commissioner Roger Goodell, however, chastised the player for showing "no meaningful remorse" for his conduct.
The NFLPA, in a statement after Henderson's ruling, said it had expected Peterson's appeal to be denied because of what it called Henderson's "relationship and financial ties to the NFL."
Henderson is a former NFL executive who dealt mostly in player and labor relations during his time with the league.
The union, in its filing on Monday, reiterated its stance that Goodell is ignoring protections in contract "in favor of issuing arbitrary and inconsistent discipline to promote the League's own public relations agenda."
The union says that Peterson was unfairly penalized under a revised personal conduct policy issued in late August, months after the incident in question occurred.
The NFL toughened its policy in response to mounting criticism over the Ray Rice domestic violence case. Rice won his appeal of an indefinite suspension levied by the commissioner in September for punching his future wife in an Atlantic City casino elevator in February.
Monday's lawsuit came as ABC News obtained an audio tape of a November 12 telephone conversation between Peterson and NFL executive Troy Vincent, in which Vincent indicates Peterson will be subject to a two-game suspension -- which was the maximum penalty for a first-time offender under the previous personal conduct policy.
During Peterson's appeal hearing, Vincent insisted he never promised Peterson anything, and Henderson agreed in his ruling, saying Vincent lacked the authority to do so.
The tape, which was part of the appeal process, has Peterson asking Vincent if he would only be penalized two games. Vincent responded, "Yeah," but added that Peterson would have to "go through the process," including a hearing which Peterson opted not to attend.
Peterson a two-time NFL rushing champion and former league Most Valuable Player, hasn't played since the Vikings' season opener September 7.