(Reuters) - The NFL Players Association filed a lawsuit against the National Football League (NFL) on Thursday alleging the appeals process in the New Orleans Saints' bounty scandal was unfair.

NFL Commissioner Roger Goodell, who banned four players in May after a probe into a program that rewarded Saints players with cash payments for knocking opponents out of games, upheld his ruling on Tuesday after holding an appeals hearing last month with the players.

"The NFL has rendered the arbitral process a fraud, refusing to provide the NFLPA with access to relevant evidence or any witnesses, while at the same time utilizing hearsay to smear and punish the players," the 526-page suit charged.

Saints linebacker Jonathan Vilma, defensive end Will Smith, defensive lineman Anthony Hargrove (now with the Green Bay Packers) and linebacker Scott Fujita (now with the Cleveland Browns) were the players punished for the upcoming season.

Vilma was suspended for the entire 2012 campaign, Hargrove received an eight-game ban, Smith was hit with a four-game suspension and Fujita got three games.

The suit asked for a neutral arbitrator to determine the validity of the players' suspensions.

Vilma had already filed a defamation suit against Goodell and another claiming the commissioner failed to make a timely appeals decision in the case.

The NFL responded with a statement.

"As in the case of Mr. Vilma's lawsuit, this is an improper attempt to litigate an issue that is committed to a collectively bargained process," the NFL said.

"There is no basis for asking a federal court to put its judgment in place of the procedures agreed upon with the NFLPA in collective bargaining. These procedures have been in place, and have served the game and players well, for many decades."