Following his clash with Parhon, Popa took the even more drastic step of resigning from the Romanian Society for Friendship with the Soviet Union. Also in 1945, he began aiding Constant Tonegaru's "Mihai Eminescu Society", a secret opposition group that distributed appeals for help to the West. He used his dean's cabinet as storage room for such anticommunist propaganda. During this period, he was attacked and robbed by a group of three Soviet soldiers, which he interpreted as a warning.