Students and faculty were notified by e-mail Sunday they must present their IDs to enter campus buildings after a threat is received, the Pittsburgh Post-Gazette reported.
Robert Hill, a spokesman for Pitt, said the university entered "crisis mode" after receiving 21 bomb threats since Feb. 13, some of which prompted evacuations of multiple buildings.
Provost Patricia Beeson and Executive Vice Chancellor Jerry Cochran sent the e-mail to students and faculty, saying, "the University will limit access to buildings once they have been swept and cleared."
The tightened security came hours after the university received a threat to the Hillman Library, Sennott Square and Benedum Hall, the Pittsburgh Tribune-Review reported.
"Not all buildings will have limited access, but over the next few days we expect this will extend to all buildings," the e-mail said. "We have made it through many complicated situations before. Thank you for your patience and dedication and know that we will get through this one together."
The new measures will reduce the time it takes to clear and reopen the buildings in the event of another bomb threat, the chancellors said.
Book bags, backpacks, laptop cases, large purses and packages will not be allowed into the buildings once they have been reopened, Hill said.
So far, no bombs have been found following any of the recent threats.