Roelfzema continued his studies during the occupation and became involved in the Dutch underground. In October the faculty at Leiden received a letter demanding to know if they were of Jewish heritage. On 23 November all the Jewish staff at the university were dismissed. The Dean of the Law School, Professor Rudolph Cleveringa, gave a speech on 26 November 1940 condemning these dismissals. He and several other of the law professors were arrested. This instigated a 48-hour strike by the students. In response the Germans closed the university.