A UCLA professor accused of sexual harassment reported receiving a threatening telephone call last week.

According to a university police log, history professor Gabriel Piterberg reported receiving an annoying, obscene or threatening phone call to police on Jan. 11.

Piterberg was accused of making unwelcome sexual advances on his graduate students in 2013. Student groups have protested his return to campus since the beginning of the quarter by disrupting his morning classes. The groups are planning to protest Wednesday.

UCPD spokesperson Nancy Greenstein said police are investigating the case and did not specify the nature of the calls.

UCLA spokeperson Tod Tamberg said in a statement that UCLA has worked to provide Piterberg and students with a safe classroom environment. He did not say whether UCLA will take additional measures to protect Piterberg if the phone calls persist.