Updated

The NFL players’ union sued the league on behalf of Dallas Cowboys star running back Ezekiel Elliott late Thursday night, seeking to vacate the upcoming ruling of an arbitrator on the appeal of the player’s six-game suspension in a domestic violence case.

The lawsuit, filed in federal court in Texas, accuses the NFL’s appeal process of being “fundamentally unfair” because arbitrator Harold Henderson denied a request to have his ex-girlfriend, Tiffany Thompson, testify at an appeal hearing that wrapped up earlier Thursday.

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Ezekiel Elliott has appealed his six-game suspension. (AP)

The suit also claimed NFL executives hid information that was favorable to Elliott before Commissioner Roger Goodell imposed the punishment on Aug. 11.

The lawsuit accused NFL lawyer Lisa Friel of withholding from Goodell the word of co-lead investigator Kia Roberts, who the suit said concluded the accuser was not credible and discipline was not warranted.

EZEKIEL ELLIOTT TO APPEAL SUSPENSION, TURN TABLES ON ACCUSER, REPORT SAYS

Roberts testified she was the only NFL staffer that interviewed Thompson while investigating the accusations. Roberts said Thompson “was not credible in her allegations of abuse,” according to ESPN. Roberts also said discipline for Elliott was not warranted.

"The withholding of this critical information from the disciplinary process was a momentous denial of the fundamental fairness required in every arbitration and, of course, does not satisfy federal labor law's minimal due process requirements," the lawsuit said.

Henderson was supposed to rule on the NFL’s decision to suspend “as soon as practicable,” according to the labor agreement.

Elliott, the NFL's 2016 rushing leader as a rookie, was suspended after the league concluded he used physical force last summer in Ohio against Thompson, his girlfriend at the time. Prosecutors did not pursue the case, citing conflicting evidence.

Elliott denied the allegations under oath in the appeal bearing, according to the lawsuit.

The lawsuit said the union and Elliott’s representatives plan to file for a temporary restraining order in hopes of making the running back eligible for the season opener against the New York Giants on Sept. 10.

The lawsuit also cited Henderson's refusal to require Goodell to testify. According to the labor agreement, Goodell can choose from a list of arbitrators for appeals.

UNION APPEALS COWBOYS RB EZEKIEL ELLIOTT’S 6-GAME SUSPENSION

The NFL’s personal conduct policy was heavily criticized three years ago for their handling of Baltimore Raven’s player Ray Rice’s domestic violence case. Rice was filmed punching his
then fiancee in the head in an elevator, knocking her unconscious. Rice was dropped from the Ravens and has not been signed since.

According to the letter Elliott received informing him of the suspension three weeks ago, the NFL believed he used "physical force" three times in a span of five days in a Columbus, Ohio, apartment last July resulting in injuries to Thompson's face, neck, shoulders, arms, hands, wrists, hips and knees.

The Star-Telegram reported that Thompson allegedly made a number of threats to Ezekiel after he told her not to come to his house on July 21, 2016. Thompson reportedly told Elliott in a text message: “Ok this is what you want? Ok then, I’m going to ruin your life. You will see. If I was you, I wouldn’t go out tonight.”

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Jerry Jones told reporters he would comment on the case when the time was right. (AP)

Prosecutors in Columbus decided about a year ago not to pursue the case in the city where Elliott starred for Ohio State, but the NFL kept the investigation open. The league said its conclusions were based on photographs, text messages and other electronic evidence.

Cowboys owner Jerry Jones did not comment on the case but said he would at a later time. "Believe you me, I will," Jones said.

The Associated Press contributed to this report.