Smarting over protests during the Tony Awards season on behalf of casting directors seeking union recognition, Broadway theater owners and producers have fired back with threats of legal action not only against the casting directors, but also against the unions that support them.

Broadway casting directors are responsible not only for casting Broadway shows but also national tours and replacements for long-running shows that can number in the hundreds, especially for large musicals. For the last year, the casting directors – including top names from Hollywood as well as Broadway such as Ellen Lewis, Bernard Telsey and Tara Rubin – have aligned themselves with International Brotherhood of Teamsters Local 817. They’ve sought to negotiate a collective bargaining agreement with the Broadway League that would be consistent with the League’s contracts with unions representing actors, stage managers, musicians, stagehands, designers, box office personnel and others.

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The League has responded by insisting that casting directors are independent contractors not employed by producers. They have urged Local 817 to seek a ruling by the National Labor Relations Board as to the legitimacy of their claim to represent the casting directors in negotiations. “The casting directors have all signed union authorization cards authorizing Local 817 to be their union,” a spokesman for Local 817 told Deadline this morning. “Employers can legally recognize the union at that point, and that is what we are asking the Broadway League to do.”

In recent weeks, Local 817 and the casting directors have upped the ante by getting support from high-profile members of the recognized Broadway unions, including actors Robert De Niro, Alec Baldwin, Bette Midler and Whoopi Goldberg, along with creatives including Hamilton‘s Lin-Manuel Miranda. Local 817 also organized a protest outside Radio City Music Hall the day before the CBS Tony Awards telecast from the storied New York venue. That action appears to have pushed the League to the brink. In separate letters to Local 817 and Broadway union legal representatives, copies of which were provided to Deadline by Local 817, League attorney Bernard Plum, of the firm Proskauer Rose LLP, referenced the Radio City protest and laid out the League’s response:

“[E]arlier today, Local 817 organized and led a picket line of more than 100 people in front of Radio City Music Hall, the sole purpose of which was to pressure League members to recognize the Union,” Plum wrote on June 8 to Local 817 attorney Stuart W. Davidson, of Willig, Williams & Davidson. “The Union’s conduct must stop immediately…the effect, if not design of, the Union’s efforts would eliminate competition among independent casting director companies. Such collective action, undertaken for the purpose of increasing the cost of casting director services, is a per se violation of the antitrust laws…Local 817 must cease and desist from any further picketing, publicity campaign, rally, or social media activities…If any such conduct occurs, the League and/or its members will file charges with the National Labor Relations Board…”

In a separate letter to attorneys for four key Broadway unions, Plum reiterated the League position, adding that, “League productions will not undertake an obligation to bargain over employment terms of employees of those companies any more than they would agree to bargain over the employment terms of employees of the numerous other independent businesses that they deal with, such as general managers, marketing companies or advertising agencies.” Plum further added that, “[W]e want to make sure you are aware of our view that — to the extent they participate in activities supportive of Local 817 — your clients stand in the shoes of that union, which means that any interruption of work, including a sympathy strike or refusal to cross a Local 817 picket line, would be unlawful under both the NLRA and federal and state antitrust laws, and would subject your clients to significant monetary liability.”

An information officer from the New York office of the National Labor Relations Board told Deadline this morning that if picketing was involved, the League “would be able to file a complaint” with the board. The union clarified, saying the event at Radio City was a rally, not a picket line. No labor action has been instigated by the casting directors.

Responding to Plum’s letters, Local 817 president Tom O’Donnell said, “Just like Donald Trump, Broadway producers need to learn that you can’t threaten to sue everyone who disagrees with you. We are talking about healthcare and retirement for 40 people in an industry that grossed $1.5 billion last year. It’s time for Broadway producers to come to the table and treat the casting directors who work for them with respect.”

The casting directors have won considerable industry-wide union support, including cast members from 20 current Broadway shows including The Book of Mormon, Hamilton, Indecent, Dear Evan Hansen, Beautiful, Hello Dolly!, Sweat, Kinky Boots, Cats, Waitress, Six Degrees of Separation, Miss Saigon, The Little Foxes, Anastasia, Bandstand, A Bronx Tale, The Phantom of the Opera and Come from Away. The powerful stagehands union also is vocal in its support.

“The 3,000 members of Local One stand firmly with all workers on Broadway, including its casting directors in their fight for union representation, health coverage, and the right to a dignified retirement,” said James J. Claffey Jr., President, I.A.T.S.E. Local One. “We believe the Broadway League has an obligation to engage and bargain with Local 817, and our union will not be intimidated or afraid of threats while offering our full support. The membership of Local One are trade unionists, and we will continue to support Broadway’s casting directors for as long as it takes for them to find justice.”

The film and television industries – most of which also now produce shows on Broadway and are members of the Broadway League – have had union contracts with casting directors for more than a decade.

Neither Plum nor the League responded to Deadline’s request for comment this morning.