Originally Published: 17 OCT 23 14:56 ET

Updated: 17 OCT 23 15:28 ET

By Matt Egan, CNN

New York (CNN) — Billionaire Ronald Lauder, a powerful financial backer of the University of Pennsylvania, is threatening to cut off donations if the school doesn’t do more to fight antisemitism, CNN has learned.

The threat from Lauder, one of the heirs to the Estee Lauder cosmetics company, marks the latest fallout from donors and alumni alarmed by a Palestinian literary festival that was held on campus last month prior to the Hamas terror attacks on Israel.

Even before the Palestine Writes Literature Festival started, UPenn leaders acknowledged it would include speakers with a history of making antisemitic remarks.

“The conference has put a deep stain on Penn’s reputation that will take a long time to repair,” Lauder wrote to UPenn President Liz Magill on Monday in a letter obtained by CNN.

“You are forcing me to reexamine my financial support absent satisfactory measures to address antisemitism at the university,” Lauder wrote.

The Palestine Writes festival has created a backlash that prominent donors, including billionaire Marc Rowan and former US Ambassador Jon Huntsman, who have vowed to cut off funding. Rowan called for Magill to resign and trustee Vahan Gureghian did step down late last week.

Lauder said he had two people taking photos at the Palestine Writes festival and two more who listened to the speakers, who were “antisemitic and viscerally anti-Israel.”

Organizers of the Palestine Writes festival denied that it embraced antisemitism, according to UPenn student newspaper The Daily Pennsylvanian.

UPenn did not respond to a request for comment on the Lauder letter, but the university has stressed it did not and does not endorse the speakers or their views.

Lauder, whose fortune is estimated at $4.6 billion, according to Forbes, serves as president of the World Jewish Congress, an organization that aims to protect Jewish communities around the world from discrimination.

“I have spent the past 40 years of my life fighting antisemitism around the world and I never, in my wildest imagination, thought I would have to fight it at my university, my alma mater and my family’s alma mater,” Lauder wrote in the letter.

Lauder, who served as the US ambassador to Austria in the 1980s, graduated from UPenn and helped start The Lauder Institute, a Wharton business program named after his father.

Lauder said he made a “special trip” to Philadelphia to meet with Magill and persuade her to cancel the Palestine Writes festival and made two subsequent phone calls in that effort.

“The timing of this event could not have possibly been worse,” he wrote.

In his letter, Lauder argued the organizers of the event came “almost exclusively” from the Department of Arts and Sciences and demanded action be taken.

“Let me be as clear as I can: I do not want any of the students at The Lauder Institute, the best and brightest at your university, to be taught by any of the instructors who were involved or supported this event,” Lauder wrote. “We know who they are and what they did.”

Magill, UPenn’s president, conceded over the weekend that the response to the Palestine Writes Literature Festival was inadequate.

“While we did communicate, we should have moved faster to share our position strongly and more broadly with the Penn community,” Magill said in a statement Sunday.

The UPenn leader said she knows how “painful the presence of these speakers” on campus was for the Jewish community, especially during the holiest time of the Jewish year.

“The University did not, and emphatically does not, endorse these speakers or their views,” Magill said.

“I want to leave no doubt about where I stand. I, and this University, are horrified by and condemn Hamas’s terrorist assault on Israel and their violent atrocities against civilians,” Magill said. “There is no justification — none — for these heinous attacks, which have consumed the region and are inciting violence in other parts of the world.”

Palestine Writes describes itself as the “only North American literature festival dedicated to celebrating and promoting cultural productions of Palestinian writers and artists.”

One organizer told CNN the festival was meant to celebrate Palestinian culture and literature.

“We wanted to honor our ancestors, celebrate our heritage. Discuss our books, talk about our predicament. Talk about resistance, talk about politics and power and culture and song and books and food and all of these things,” Susan Abulhawa, executive director of the Palestine Writes Literature Festival, told CNN.

Abulhawa, an author who isn’t affiliated with UPenn, described the event as “glorious” and “so beautiful people were in tears.”