The negotiations between the Professional Soccer Referees (PSRA) -- the union that represents officials that work MLS matches -- and its employer, the Professional Referees Organization (PRO), are becoming increasingly acrimonious, with PRO filing an Unfair Labor Practice (ULP) charge against the PSRA earlier this week.

The filing, a copy of which has been obtained by ESPN, alleges that PSRA executive board member Chris Penso "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."

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The charge comes amid a lockout by PRO of PSRA referees that was instituted after the union voted overwhelmingly to reject a tentative collective bargaining agreement negotiated between representatives of the two organizations. 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 PSRA is seeking increases in compensation as well as improved travel accommodations.

The MLS regular season began on Wednesday with the league using a replacement officiating crew for Inter Miami and Lionel Messi's win over Real Salt Lake. A full slate of games is set for this weekend with replacement referees coming from the professional, college and youth ranks.

CBA talks are scheduled to resume next Wednesday in New York City, with a federal mediator present.

The ULP document goes on to allege that Penso and other bargaining unit and PSRA members have revoked college assignments of replacement officials.

"College soccer officiating assignments are outside employment unrelated to the operations of PRO, and Mr. Penso, as well as numerous other bargaining unit and PSRA members, are responsible for assigning such work for third parties," the document states.

The document also alleges that on or about Feb. 18, 2024 and continuing thereafter, other agents of PSRA, including bargaining unit and PSRA members, "threatened replacement workers with reprisals for engaging in replacement work during a lockout, including, but not limited to, loss of outside employment (i.e., college officiating assignments and other non-bargaining unit work); loss of reputation and future opportunities to officiate PRO-assigned matches; exclusion from the social and professional officiating community; and other explicit and implicit threats for engaging in work of the PSRA bargaining unit during a work stoppage, which is protected under Section 7 of the National Labor Relations Act ("NLRA")."

The PSRA had previously filed two ULP charges against PRO. 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 PRO's general manager, Mark Geiger, sent a letter to union membership on Feb. 9 stating that if the tentative agreement wasn't approved, it would lock the players 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."

Contacted by ESPN following the disclosure of PRO's filing, PSRA president Peter Manikowski said: "The union is reviewing [the document], and we want to reiterate that the National Labor Relations Board is investigating the two Unfair Labor Practice charges that we filed in January and February."

PRO's ULP filing comes amid the two sides trading accusations about the bargaining process. Prior to Wednesday's season opener between Miami and Real Salt Lake, MLS commissioner Don Garber told reporters that the rejection of the tentative agreement amounted to "a very disappointing process."

"I can't remember in my nearly 40 years of sports ever having a bargaining unit reach agreement and then not having the members support it," he said.

The PSRA hit back on Thursday stating, among other things, that its negotiators repeatedly told their PRO counterparts that what was being offered wouldn't be approved by its membership, and only put the tentative agreement to a vote because they were told "there is no more money," and needed to drive home how inadequate the proposal was. It also described a proposed no strike/no lockout agreement as inadequate given that it would have frozen wages at 2023 levels.

This drew a response from Geiger that the PSRA had mischaracterized his letter to union membership, and that he was simply conveying what would happen if the deal was rejected. Geiger added that the offer of paying PSRA members the same wage during negotiations was required by U.S. labor law, and would take place as negotiations continued.