The union filed a grievance late Thursday, one day after Goodell suspended four players who participated in bounties from 2009-11. The complaint says Goodell is prohibited from punishing players for any aspect of the case occurring before the new collective bargaining agreement was signed last August. It argues that a CBA system arbitrator, and not Goodell, has the right to decide player punishment under such circumstances, as well as rule on any appeals.

In a document obtained by The Associated Press, the union told the league Goodell "released all players from conduct engaged in prior to execution of the CBA."

"Thus, even assuming for the sake of argument that the commissioner had the authority to punish players for conduct detrimental under the alleged facts and circumstances of this particular situation — he does not — he nevertheless would be prohibited from punishing NFL players for any aspect of the alleged ‘pay-for-performance/bounty’ conduct occurring before Aug. 4, 2011," the union said.

Last August, the league agreed not to file lawsuits against players regarding detrimental conduct that occurred prior to signing the new CBA. But the clause the union cites doesn’t deal with conduct detrimental to the league that endangered player safety over three seasons.

Earlier this week, Goodell suspended linebacker Jonathan Vilma for the 2012 season; defensive lineman Anthony Hargrove, now with Green Bay, for eight games; defensive end Will Smith, for four games; and linebacker Scott Fujita, now with the Cleveland Browns, for three games.

The union said the suspensions violate the league’s "duty of fairness to players," and that the process "violated various procedural requirements of the collective bargaining agreement, including limits of Goodell’s authority over the matter and failure to disclose sufficient evidence of the violations."

The league said its investigation showed "a significant number of players participated" in the bounty system — by ponying up cash or collecting it — but noted that "the players disciplined participated at a different and more significant level." The league said anywhere from 22 to 27 Saints players participated.

The suspended players haven’t filed appeals, league spokesman Greg Aiello said Friday. The deadline is Monday and Vilma and Smith have already said they plan to file.

Aiello said the union is seeking immunity for the four suspended players, "a position it never advanced during the months of discussion on this matter."

The union letter said the NFL must begin proceedings before arbitrator Stephen Burbank, a University of Pennsylvania law professor, and that he "would ultimately determine whether and to what extent the players should be punished."

"We expect that the arbitrators will reject the union’s efforts to protect players from accountability for prohibited and dangerous conduct directed against other players," Aiello said, "and uphold the disciplinary process that was so carefully negotiated in the Collective Bargaining less than a year ago."

Even if the arbitrator finds that Goodell had the authority to punish the players, the union maintained that appeals for on-field behavior should be heard by Art Shell and Ted Cottrell, not Goodell. Shell and Cottrell are employed by the NFL and the NFLPA as independent hearing officers when players are fined or suspended for flagrant hits during games.

The union also urged an expedited hearing of its grievance before another arbitrator, Shyam Das, on May 16.

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AP Sports Writer Richard Rosenblatt contributed to this story.