Barring a sudden agreement, the 2024 MLS season opener on Wednesday featuring Argentine great Lionel Messi's Inter Miami will be officiated by replacement referees.
"On the eve of the 2024 MLS season, attention should be focused on the competition on the field," the MLS Players Association said in a statement.
"The use of replacement referees will not only negatively impact the quality and results of our matches, it may also jeopardize the health and safety of players."
The MLSPA called the lockout and use of replacement referees a "step backward" for MLS and said all workers deserve a fair wage, safe working conditions and the ability to collectively bargain in good faith.
It also urged all sides involved to return to the bargaining table and work towards a timely and fair agreement.
The Professional Referee Organisation (PRO) said on Saturday it decided to lock out MLS referees after the Professional Soccer Referees Association (PSRA) rejected a proposed new labor pact.
PRO last locked out MLS referees over labor talks in 2014, when replacement officials were used for the first two weeks of the season.
The PSRA said feedback from members indicated the failed ratification was driven by issues with the compensation and benefits PRO was offering, as well as a lack of improvements to travel, scheduling and other quality-of-life issues.
According to the PSRA, 97.8% of its membership participated in the vote, with 95.8% voting to reject ratification of the tentative agreement.
The PSRA also said replacement officials do not have the experience and fitness required to do the job properly and that players, coaches and fans deserve referees who best know the MLS game and its rules and applications.
According to MLS, the tentative agreement that was reached would have made PRO members among the highest paid soccer match officials in the world.
