The NFL resumed talks with the locked-out referees on Sunday, but the meeting broke off without a deal and significant differences remain, according to NBC Sports' Peter King.
There are no more formal negotiations scheduled and the sides reportedly remain far apart on details including salary, retirement benefits and operational issues.
The regular referees have been locked out since June.
The NFL Players Association executive committee posted an open letter on Sunday criticizing the NFL owners for using replacement referees.
The letter was titled, "Your Lockout of the NFL Referees and the Negative Impact on Football" and was signed by NFLPA president Domonique Foxworth and several current players including Saints quarterback Drew Brees, the NFLPA Vice President .
The letter called for an end to the lockout, and ripped the owners for allowing inexperienced replacement refs to work games, which has "led to a deterioration of order, safety and integrity." The NFLPA claimed the situation has created embarrassing headlines and was heavily critical of the league allowing Commissioner Roger Goodell to "cavalierly" issue fines and suspensions in an effort to improve player safety while alloing the referee lockout to drag on.
The NFLPA letter in its entirety:
"The NFL Players Association Executive Committee is calling on you to end the lockout of our referees. We believe there is substantial evidence that you have failed in your obligation to provide as safe a working environment as possible.
Your decision to lock out officials with more than 1,500 years of collective NFL experience has led to a deterioration of order, safety and integrity. This affirmative decision has not only resulted in poor calls, missed calls and bad game management, but the combination of those deficiencies will only continue to jeopardize player health and safety and the integrity of the game that has taken decades to build.
"As we predicted and explained to you weeks ago, the removal of the veteran officials from regular season games left a group of your replacements who have proved to be incapable of keeping pace with the speed of the game. Coaches and players have complained of numerous errors and failures including: erratic and missed calls on egregious holds and hits, increased skirmishes between players and confusion about game rules. Many replacements have lost control of games due to inexperience and unfamiliarity with players and rules.
"The headlines are embarrassing: a scab working a game despite having been on the payroll of one of the teams, another who was assigned to referee a team he publicly supported on Facebook, and one who is a professional poker player when you propose even more stringent player rules on gambling.
"It is lost on us as to how you allow a Commissioner to cavalierly issue suspensions and fines in the name of player health and safety yet permit the wholesale removal of the officials that you trained and entrusted to maintain that very health and safety. It has been reported that the two sides are apart by approximately $60,000 per team. We note that your Commissioner has fined an individual player as much in the name of "safety." Your actions are looking more and more like simple greed. As players, we see this game as more than the "product" you reference at times. You cannot simply switch to a group of cheaper officials and fulfill your legal, moral, and duty obligations to us and our fans. You need to end the lockout and bring back the officials immediately.
"We are all men who love and respect this game and believe that it represents something beyond just money. For our teammates, our coaches and our fans who deserve better, vote to end this lockout now."