At least 13 Historically Black Colleges and Universities received bomb threats on Tuesday (Feb. 1), the first day of Black History Month. According to CNN, a growing list of schools were forced to lock down or postpone classes after receiving threats.

A spokesperson for Coppin State University in Baltimore, Maryland told CNN that an unidentified individual called the school on Tuesday and said there was a bomb on campus. The threat was immediately reported to campus police and students at the school were told to shelter in place.

Other colleges, such as Morgan State University, which is also in Baltimore; shut down campus after receiving threats.

“Due to a bomb threat, access to campus will be closed as the University works with emergency personnel to assess the situation,” Morgan State University tweeted on Tuesday morning. “Everyone on campus should shelter in place until further notice. All instruction will be remote and all employees should telework.”

On Twitter, Jackson State University notified students that it received a bomb threat at 4:15 a.m. local time on Tuesday morning. The Jackson Police Department and Jackson State University Department of Public Safety did a sweep of the campus and later issued an all-clear.

According to CNN, school officials at Mississippi Valley State University, Alcorn State University, Tougaloo College, Kentucky State University, Fort Valley State University, University of the District of Columbia, Spelman College, Xavier University and Edward Waters University also reported bomb threats on Tuesday.

As reported by REVOLT, at least six HBCUs said they received bomb threats on Monday (Jan. 31), prompting campus shutdowns and class cancellations. One of those colleges was Howard University, which was also targeted with a threat on Tuesday.

“The Metropolitan Police Department (MPD) and the Howard University Department of Police have issued an ‘ALL CLEAR’ in the investigation of a bomb threat made this morning at approximately 2:55 a.m.” the Washington, D.C. college tweeted at 7:30 a.m. EST, also lifting that shelter-in-place directive at that time.

At least seven HBCUs were also forced to order lockdowns and cancel classes after receiving bomb threats on Jan. 5. No active explosive devices were located at any of the campuses after initial investigations.