The night before Dr. Joanne Liu was scheduled to deliver a long-planned speech at N.Y.U. Langone Health, the hospital affiliated with her alma mater, she received a call that stunned her. Her presentation on humanitarian crises was being canceled, the university official on the other end of the line said.

The reason, Dr. Liu said she was told, was that her presentation could be perceived as antigovernment and antisemitic.

To Dr. Liu, a professor at McGill University in Montreal and a pediatric…