Hernandez, 23, was released by the New England Patriots in June after he was indicted on a murder charge, CNN reported.
"On behalf of all players, it is our responsibility to protect the rights in collective bargaining agreement. We are not tone-deaf to what the allegations are in this case, but for the benefit of all players, there are important precedents here we must protect," the player's union said in a statement Tuesday.
His grievance is one of about 70 payment grievances filed by the union against the NFL, union spokesman Carl Francis said.
The Bristol County, Mass., District Attorney's Office announced Tuesday Hernandez will be arraigned Sept. 6 on first-degree murder charges in Fall River Superior Court.
He has been held without bail since June 26, when he was charged in the death of Odin Lloyd, 27. Lloyd's body was found riddled with bullets near Hernandez' North Attleboro, Mass., home on June 17, the Boston Herald said.