The NFL Players Association filed a lawsuit against the National Football League on Monday challenging an arbitrator's decision to uphold the league's suspension of Minnesota Vikings running back Adrian Peterson.

Filed at the U.S. District Court in Minneapolis, the lawsuit claims arbitrator Harold Henderson, a former NFL executive hand-picked by Commissioner Roger Goodell to hear the case, was not impartial.

Henderson on Friday upheld Goodell’s unpaid suspension of Peterson until at least April 15th, saying Peterson “has not demonstrated that the process and procedures surrounding his discipline were not fair and consistent.”

Peterson, 29, pled no contest to a misdemeanor reckless assault charge last month for injuring his 4-year-old son in May while disciplining him with a wooden switch.

After the no-contest plea, Goodell ruled that Peterson, the NFL’s most valuable player in 2012, will not be allowed back on the field until April 15th at the earliest.

Misinformed

When the NFLPA filed an appeal, Goodell chose Henderson, a former NFL executive vice president of labor relations, to hear the case. Henderson has heard 87 appeals involving personal conduct and drug issues.

Peterson, in appealing Goodell’s suspension, claimed he had been told by NFL executive Troy Vincent that he would only be suspended two games.

ABC News released audio tape on Monday November 12th of a telephone conversation Peterson had with Vincent, concerning how long Peterson would be kept off the field.

“It will be two additional games, not time served?” Peterson asks during the conversation.

“No, no, no, no ... it won’t ... The one this weekend,” Vincent responds. “So really, it’s just next week and you ... will be back.”

Six days later, Goodell handed down his suspension.

Henderson, in his ruling, said Vincent did not promise a two-game suspension and, as the NFL’s vice president for football operations, had no authority to do so.

The union claims the NFL retaliated against Peterson for not meeting with the league days before his suspension, a get-together the union says the six-time All-Pro was not required to attend.

“This is another instance in which the National Football League will say anything on one day and do anything on another day to try to support a position that at this point is completely devoid of any rationality,” NFLPA Executive Director DeMaurice Smith told ESPN Radio on Monday.

Peterson has played in only one game this year.