The Professional Soccer Referees Association (PSRA) - the union which represents officials used for MLS - has rejected a deal proposed by the Professional Referees Organization (PRO) and now faces being locked out from midnight on Saturday.
The breakdown comes just days ahead of the start of the new MLS season, which kicks off Wednesday when Lionel Messi's Inter Miami host Real Salt Lake.
If no deal is reached by the time the new season starts, MLS will be forced to hire referees who are not part of the union.
The PSRA said on Saturday that 97.8 per cent of its membership had voted on a deal put forward by PRO, with 95.8 percent voting to reject. PSRA said the deal fell "short of expectations, along with a lack of quality of life improvements."
"We live for this game, giving it 100 per cent of our dedication, experience, fitness and ability," PSRA president and chief negotiator Peter Manikowski said in a statement.
"The skyrocketing growth of MLS has significantly increased demands on officials mentally and physically, and as such has increased demands on both our professional and personal time.
"Our members are asking not only for fair compensation at a time when the league is reporting record growth, but also for the ability to take care of themselves on the road and at home to continue officiating at the highest level that this sport demands."
The referees' previous five-year deal expired in January.
Mark Geiger, general manager of PRO, said referees had been offered pay increases which represented a 25 per cent overall increase from 2023 in terms of salary, retainers, game fees and benefits.
"The result of the membership vote is disappointing," Geiger said in a statement.
Geiger added that the PSRA had rejected a no strike/no lockout proposal which would have allowed referees to officiate while negotiations were ongoing.
That decision means qualified non-union replacement referees are now poised to take charge of MLS games starting next week.
"We are left with no choice but to institute a lockout and use qualified non-bargaining unit officials so that games can go ahead as scheduled," Geiger added.
Manikowski meanwhile said using replacement refs would be a mistake.
"We think replacement officials generally do not have the current experience and level of fitness required to do our jobs," Manikowski said in a statement.
"The sport and everyone involved - players, coaches and fans - deserve referees who are the best in North America at knowing the MLS game and its current rules and applications."
