The NFL Players Association has officially appealed Minnesota Vikings running back Adrian Peterson's NFL suspension.

They have also demanded an independent neutral arbitrator.

"Moreover, given the intense criticism that you and the League office have faced from NFL business partners, Congress, the media, NFL fans and the public at large, and the public pronouncements and commitments you have personally made in response to this criticism, it is clear that you have, by your actions, rendered yourself evidently partial and biased in this matter," the players' union wrote in a letter to Goodell.

Peterson is suspended without pay for at least the rest of the season and won't be considered for reinstatement until April 15, 2015 at the soonest. Peterson plead no contest to misdemeanor reckless assault in Texas for hitting his four-year-old son with a wooden switch.

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Aaron Wilson covers the Ravens for The Baltimore Sun</p>