The Giants on Tuesday suspended Burress for four games and fined him in the wake of an incident last weekend in which the player apparently shot himself in the leg while at a New York nightclub.
Team doctors said the wound would have kept Burress out of the lineup for 4-6 weeks.
He was placed on the reserve non-football injury list, which bars him from practicing or being on the team's active roster for the remained of the 2008 regular season and the playoffs.
Burress has been charged with two counts of second-degree criminal possession of a weapon. If convicted he could be sentenced to 15 years in prison. He posted $100,000 bond when arraigned Monday and has a March 31 court date.
A statement Thursday on the NFLPA Web site said, "The NFLPA is still reviewing the actions taken by the New York Giants relating to Plaxico Burress but we intend to file a grievance challenging those actions as we believe that Burress' rights have been violated under the (collective bargaining agreement)."