(CNN) — Rep. Alexandria Ocasio-Cortez and Sen. Elizabeth Warren will no longer participate in The New Yorker Festival in an act of solidarity with the magazine’s staff union.

The New Yorker union is holding a digital picket at 8 p.m. ET on October 5 — the day Ocasio-Cortez and Warren were originally scheduled to speak at the event — to call attention to its fight for a just cause proposal in its union contract. Just cause is a labor protection that requires an employer to build a case for why an employee should be fired.

“The NewsGuild and The New Yorker Union are fighting for basic dignity on the job and we stand with them,” Ocasio-Cortez and Warren said in a joint statement shared with CNN Business. “We will not cross the picket line and attend the festival unless The New Yorker leadership agrees to the union’s demands — they should do so immediately.”

The annual New Yorker Festival features conversations with celebrities, politicians and other high-profile speakers. This year’s speakers include Dr. Anthony Fauci, Margaret Atwood and Malcolm Gladwell. The event is being held virtually because of the pandemic and runs from October 5 to 11. V.I.P. passes, which include access to the majority of the events, cost $51.45. Priced individually, most talks cost $19.95. Subscribers to The New Yorker get 40% off.

The NewsGuild of New York, which represents The New Yorker union, sent letters to both Ocasio-Cortez and Warren on September 24. The letters asked each of them to withdraw from the festival and join the picket line, citing their support for unions and workers.

“The leadership that you both display on issues like labor rights and corporate responsibility brings hope at a time when it’s hard to come by. Because of your strong support for unions and workers, we thought it important to let you know that The New Yorker is in a state of labor unrest,” the letter reads.

Staffers at The New Yorker announced their intention to unionize in June 2018, joining a wave of media companies that have organized to seek better workplace protections. David Remnick, who has served as editor of The New Yorker since 1998, recognized the union a month later. But over the past few months, staffers in the union have been demanding the company add just cause to the contract, and have organized a half-day work stoppage and an online campaign in June as part of that effort.

“Many of our members work on The New Yorker Festival each year,” Natalie Meade, unit chair of The New Yorker union, said in a statement. “We also work overtime—often without pay—to publish a magazine, a website, and more. But our managers refuse to grant us just cause, which would be a signal of mutual respect and dedication.”

Ticket holders to the event that was to feature Ocasio-Cortez and Warren have been issued refunds, according to a New Yorker spokesperson. The spokesperson acknowledged the dispute over the just cause proposal in a statement to CNN Business.

“For more than two years, New Yorker management has been meeting with the union regularly in good faith to discuss its just-cause proposal and other contract proposals,” the spokesperson said. “In that time, we have worked with them to implement several important provisions regarding diversity, hiring, and other matters. Critically, however, the union has yet to present us with core economic proposals that are central to any contract, which has made it impossible to reach an overall agreement.”

“Like many other media outlets, The New Yorker strongly believes that its editorial standards should not be determined by arbitrators outside of The New Yorker, and we look forward to our continued discussions regarding just cause in the context of bargaining. We remain eager to reach a fair agreement as quickly as possible,” the spokesperson added.

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