Five Harvard Business School alumni including US Senator Mitt Romney and hedge fund manager Seth Klarman criticized Harvard University over its response to protests by pro-Palestinian demonstrators, saying the school ignored the safety of Jewish students.

“Your silence as the situation intensifies is both astounding and frightening,” they wrote in an “Open Letter to Harvard Leadership Regarding Antisemitism on Campus” that was addressed to the university’s president, Claudine Gay, and other leaders. “Given that Harvard has been vocal in its advocacy for the rights of students from other religious, racial and ethnic groups, this silence, amidst the meteoric rise in antisemitism, is deafening.”

The letter, in which Romney, Klarman and their co-signers cited “threatening, violent protests” on campus, adds new fuel to the controversy swirling around Harvard over its handling of the fallout from Hamas’s attack on Israel. Larry Summers, a former Harvard president, said earlier this month that he was outraged by Harvard’s initial silence after more than 30 student groups issued a statement blaming the attack on Israel and not Hamas, which is designated a terrorist organization by the US and the European Union.

Harvard didn’t immediately respond to a request for comment.

Around 500 protesters supporting Palestinians walked out of class and marched through multiple Harvard schools last Thursday, according to the Harvard Crimson. The newspaper said that was the third protest on campus in support of Palestinians following the start of the war in Israel and Gaza. The Crimson didn’t mention incidents of violence or arrests at the demonstration.

The statement backed by Klarman and Romney, a Utah Republican who previously served as governor of Harvard’s home state of Massachusetts, was also signed by Joanna Jacobson, Bill Helman and Mark Nunnelly.

At least two billionaire donors, Idan Ofer and Leslie Wexner, have pulled their support from Harvard.