With growing support from Broadway unions and individual celebrities including Liam Neeson, casting directors and their allies will rally Thursday morning outside Radio City Music Hall, during a rehearsal for Sunday night’s CBS telecast of the Tony Awards. The casting directors are seeking union recognition and contract negotiations with the Broadway League, which represents theater producers and owners.

Casting directors are the only Broadway workers without a union, the group says, and don’t receive medical, retirement and other benefits from the plays they work for. Casting directors have linked up with Teamsters Local 817 and are calling on Broadway producers to negotiate a union contract. The League so far has responded by telling the group to seek arbitration before the National Labor Relations Board.

The rally, scheduled for 9 AM, comes as leading actors including Neeson, Sara Bareilles of Waitress and Katrina Lenk of Indecent voice their support for the casting directors on social media, with the hashtag #FairnessForCasting. Cast members of The Book of Mormon, Hamilton, Cats, Beautiful, Bandstand, A Bronx Tale and Come from Away also have posted photos in support of the #FairnessForCasting campaign. The move also has the support of the other Broadway unions, including Actors’ Equity, the stagehands (IATSE), musicians (AFM) and directors and choreographers (SDC).