Citing the threat to the student body’s “physical and mental safety,” 177 professors at the University of California, Berkeley, have signed an open letter calling for a boycott of the campus’ so-called “Free Speech Week.

The speakers scheduled for the week—from Sept. 24 to 27— reportedly include Milo Yiannopoulos, Steve Bannon and Ann Coulter.

The San Francisco Chronicle described the event as “four days of rallies and speeches.”

The report said that—even without the boycott—it is unclear if the event will go through. Organizers did not pay for the facilities, the report said. The price tag for such an event is expected to be exorbitant. It cost $600,000 to secure a recent speech by conservative Ben Shapiro.

The letter from the professors said the event forces some students to risk their “physical and mental safety in order to attend class.”

A spokesman for the school told the paper that faculty members can decide where or when to teach their classes.

The Daily Californian, the student newspaper, reported that only five professors who teach STEM courses on campus signed the letter.

Michael Cohen, a co-author of the letter, said the amount of STEM professors on the letter does not show any differences of opinions. The letter was released last week, and they could still join. He told the paper that the humanities buildings are near where these protests often take place.

Kristie Boering, a chemistry professor, told the student paper that she plans on holding her class as planned.

“I have a job to do,” she said.