The labor impasse over a new collective bargaining agreement involving the union that represents MLS referees and their employer -- the Professional Referee Organization (PRO) -- looks set to continue, sources tell ESPN, with PRO extending its lockout of the union referees for a second round of matches this weekend.

PRO informed members of the Professional Soccer Referees Association (PSRA) on Friday that the tentative agreement negotiated by PRO and the PSRA board prior to the start of the season -- one that was rejected by 95.8% of the union membership -- remains PRO's best offer.

- Stream on ESPN+: LaLiga, Bundesliga, more (U.S.)

"After a further bargaining session on Friday, PRO has today reaffirmed that the terms of the prior agreement reached between PRO and PSRA on February 13 remain open for ratification by PSRA's membership," PRO told ESPN via email.

A deadline of midnight ET on March 11 was given to the PSRA, at which point "PRO's next offer will include less favorable terms in some areas."

PSRA president Peter Manikowski responded: "We expected this from [PRO] and we expected the company's bullying tactics, and we expected the company to continue to not listen to the members in the rejection of the first tentative agreement. And the members expected this, and the union committee expected this, and we will deal with it accordingly."

The two sides met on Wednesday and Friday of this week alongside federal mediators. On Wednesday the PSRA sent a revised offer to PRO that included significant pay increases, improved travel benefits, as well as compensation for the image and likeness fees and retroactive wage payments. That proposal was rejected. In response, PRO sent the aforementioned tentative agreement back to the PSRA.

In a letter to the PSRA membership from PRO general manager Mark Geiger, a copy of which was obtained by ESPN, Geiger said in reference to the PSRA proposal: "We were dismayed that PSRA proposed $3 million above our prior agreement, just for 2024, and far greater increases for subsequent years of the CBA ...This is simply unrealistic."

Geiger's letter added: "We hope that it will not be necessary to withdraw that best offer and substitute our less attractive alternative proposals."

In a memo to the MLS Board of Governors, MLS executive vice president Nelson Rodriguez said that 17 additional referees were being added to pool of replacement referees for this weekend's matches.

"Also, there have been numerous former professional and international match officials who have contacted PRO during the last week about working MLS matches," he added.

With regard to the CBA negotiations, Rodriguez's memo said that the PSRA offer asked for a 77% increase in compensation from 2023 "in wages, benefits, taxes, retirement benefits, and new travel upgrade costs. They also requested an increase in the likeness fee and retroactive wage payments to their members during the lockout. Remarkably, the proposal seeks greater increases than one the PSRA leadership proposed in January."

Manikowski took issue with Rodriguez's numbers, stating that the increase is 51%, which he added is "in line" with player wage increases of 55% since 2019.

The PSRA referees have been locked out since Feb. 18. This marks the second time in the last 10 years that PRO, which is funded in part by MLS, has locked out the PSRA referees during CBA negotiations.

The two sides have also accused each other of unfair labor practices. A week ago, PRO alleged that PSRA members "unlawfully threatened and coerced potential replacement workers by threatening them that performing officiating work during a lockout would negatively impact the officials' eligibility for assignments to officiate college soccer matches."

The PSRA has filed two Unfair Labor Practice (ULP) charges. The first filed back on Jan. 5, alleged that PRO representatives spoke directly with union members about the CBA talks without union leadership present, a tactic known as "direct dealing."

The second ULP charge, filed earlier this month, alleges that Geiger sent a letter to union membership on Feb. 9 stating that if the tentative agreement wasn't approved, it would lock the referees out, withdraw its current proposal and agree only to substantially inferior terms. The PSRA complaint contends this constitutes "regressive bargaining, violates [PRO's] obligation to bargain in good faith, and constitutes reprisals against PSRA members for engaging in protected activity."