In explaining the decision via a letter, Goodell wrote, "Because protecting the integrity of the game is the Commissioner's most important responsibility, I decline to rewrite our Collective Bargaining Agreement to abrogate my authority and 'discretion' to hear 'any appeal' in a conduct detrimental proceeding."
The decision was widely expected. Two weeks ago, attorneys for Goodell had formally recommended that he reject the NFLPA's request that he step aside as arbitrator.
At the NFL's spring meeting in San Francisco on May 20, Goodell said that he looked forward to hearing "directly from Tom if there is new information or there is information that can be helpful to us in getting this right." Goodell had cited his role as arbitrator as part of a "long-established" process.
The NFLPA's motion asking Goodell to recuse himself cited "a process that has contained procedural violations of our collective bargaining agreement." The union called Goodell a "central witness in the appeal hearing," adding that he is not impartial. The NFLPA wanted a neutral party to serve as an arbitrator.
Brady was suspended last month for the first four games of the 2015 season for his role in the use of underinflated footballs in the AFC Championship Game in January. The Patriots also were fined $1 million and stripped of two draft picks -- a first-rounder in 2016 and a fourth-rounder in '17.
Patriots owner Robert Kraft said last month he will not appeal those penalties.
Brady has hired attorney Jeffrey Kessler, who has taken on the league in a variety of other cases throughout the years, and could take his case to court should his punishment not be reduced after appeal.