In a letter shared with Bloomberg, Rowan pressed his fellow alumni to withhold donations to the university until two of its senior leaders step down.

“I call on all UPenn alumni and supporters who believe we are heading in the wrong direction to ‘Close their Checkbooks,’” he wrote, urging recipients to do so until Elizabeth Magill, the university’s president, and Scott Bok, chair of its board of trustees, resign.

He accused the pair of tolerating anti-Semitic attitudes at the university.

“It is time for the trustees to begin moving UPenn in a new direction,” Rowan wrote. “Join me and many others who love UPenn by sending UPenn $1 in place of your normal, discretionary contribution so that no one misses the point.”

Rowan is the cofounder and CEO of Apollo Global Management, one of America’s biggest private equity firms, and a graduate of the University of Pennsylvania’s Wharton business school. The multibillionaire and his wife donated $50 million to Wharton in 2018. His spokespeople were not immediately available for comment when contacted by Fortune.

For weeks, the University of Pennsylvania has been at the center of anti-Semitism allegations—even before Hamas’s multifront attacks on Israel over the weekend—over its hosting of a Palestinian literature festival on Sept. 22.

Two days ago Magill criticized the “abhorrent” attacks in Israel, while Bok has pledged a change in policy.

In a statement emailed to Fortune on Thursday, Julie Platt, vice chair of the University of Pennsylvania’s board of trustees, said she stood behind Magill and Bok.

“The university has publicly committed to unprecedented steps to further combat anti-Semitism on its campus, reaffirmed deep support for our Jewish community, and condemned the devastating and barbaric attacks on Israel by Hamas,“ she said. “The executive committee of Penn’s board of trustees has unanimously endorsed the actions taken by the university, and I have full confidence in the leadership of president Liz Magill and chair Scott Bok.”

An exchange of ‘controversial’ ideas

The Palestine Writes festival, advertised as a celebration of Palestinian culture’s richness and diversity, featured controversial figures like Roger Waters, the renowned British rock star from Pink Floyd, who has faced allegations of anti-Semitism. It also included Marc Lamont Hill, an academic and former CNN contributor, who was let go from the network in 2018 following a speech in which activists claim he used coded language advocating for the destruction of Israel.

Both Hill and Waters have denied accusations of anti-Semitism in the past.

Other speakers and sponsors of the event were also associated with the airing of anti-Semitic views in the past, leading to major backlash over its lineup.

“Why is UPenn hosting a festival of anti-Semites?” an op-ed featured in The Hill was headlined ahead of the event.

In his letter, Rowan—who is chairman of the board of advisors at UPenn’s Wharton business school—said the Palestine Writes festival had featured “well-known anti-Semites and fomenters of hate and racism.”

He also argued that Magill had taken no action to condemn the event’s anti-Semitic rhetoric.

Magill and Bok did not respond to Fortune’s requests for comment.

Pledging policy changes at UPenn

In a statement issued ahead of the literature festival, Magill defended the decision to hold the event on campus but noted that the festival had not been organized by the university.

“While the festival will feature more than 100 speakers, many have raised deep concerns about several speakers who have a documented and troubling history of engaging in anti-Semitism by speaking and acting in ways that denigrate Jewish people,” she said. “We unequivocally—and emphatically—condemn anti-Semitism as antithetical to our institutional values.”

However, she added that UPenn also “fiercely supports the free exchange of ideas.”

“This includes the expression of views that are controversial and even those that are incompatible with our institutional values,” she said.

In a Sept. 20 letter to Jonathan Greenblatt, CEO of the Anti-Defamation League, about the Palestine Writes event, Magill also pledged to incorporate anti-Semitism awareness into inclusion training for faculty and students.

“We will redouble our work with student organizations and other groups to encourage efforts to understand the interconnectedness of different forms of bigotry and oppression,” she said.

Meanwhile, Bok said in a statement earlier this month that the university would review its policies on allowing external organizations to host events on campus in light of the criticism of the Palestine Writes festival.

However, he noted that any policy updates would not include vetting potentially controversial speakers before giving them a platform at the university.

“That wouldn’t be appropriate,” he said, according to the Philadelphia Inquirer. “But our president has indicated that the university will look at some administrative processes to be better aware of who is coming to campus, particularly for large-scale events.”

Harvard controversy

The University of Pennsylvania is not the only prestigious college in America that has faced allegations of anti-Semitism in recent weeks, particularly in the wake of the violent attacks on Israeli civilians carried out by Palestinian militant group Hamas last weekend.

Former U.S. Treasury Secretary Larry Summers, who served as the president of Harvard University from 2001 to 2006, said on Monday he was “sickened” by the institution’s lack of response to the attacks in Israel.  

“In nearly 50 years of Harvard affiliation, I have never been as disillusioned and alienated as I am today,” he wrote in a series of tweets. “The silence from Harvard’s leadership so far, coupled with a vocal and widely reported student group’s statement blaming Israel solely, has allowed Harvard to appear at best neutral towards acts of terror against the Jewish state of Israel.”

On Wednesday—after incumbent Harvard president Claudine Gay issued a statement denouncing the Hamas attacks and distancing the university from a controversial statement signed by multiple Harvard student groups—Summers said he was “glad” and that he “hopes other university leaders will now do the same.”

Rowan said in the letter he shared with Bloomberg that he had drawn “sickening parallels” between UPenn and Harvard.

Magill said in an Oct. 10 statement that she was “devastated” by the weekend’s events.

“Many members of our community are hurting right now,” she said. “Our thoughts are especially with those grieving the loss of loved ones or facing grave uncertainty about the safety of their families and friends.”

Rowan’s call for alumni to cut donations to UPenn comes as the Israel-Gaza conflict continues to intensify in the wake of the weekend’s events.

Israel has vowed to withhold water, electricity, and fuel from Palestinians in Gaza until all Israeli hostages taken by Hamas have been released. The Israeli government has also launched a series of retaliatory air strikes at Gaza, which authorities said on Thursday have killed more than 1,300 people.

The death toll from the weekend’s attacks has reached 1,200.

U.S. Secretary of State Antony Blinken visited Israel on Thursday, where he reiterated America’s commitment to the alliance between the two nations.