The University of Pennsylvania's president is under fire from campus police for participating in a student "die-in" protest.

The head of the campus police union says officers were outraged by Amy Gutmann's display Tuesday after student protesters interrupted her holiday party.

Gutmann joined students in lying on the floor for a symbolic 4 1/2 minutes as they protested the police-shooting death of Michael Brown in Ferguson, Missouri.

Union chief Eric Rohrback says in Friday's Philadelphia Inquirer that Gutmann gave in to the "uninformed mob mentality." He called it a "slap in the face."

A Penn vice president says Guttmann was showing solidarity with students, not attacking officers.

Penn State President Eric Barron gave a similar explanation amid calls that he apologize for making the "hands up" gesture during a protest.