Natan Slifkin said this about the ban against several of his books
It appears that the primary person [Initiating the ban] was Rabbi Yaakov Kalmanowitz. He was someone strongly opposed to “secular thinking” – recordings of him on this topic can be downloaded here (Part One and Part Two). But I was also reliably informed that his primary opposition to my works was not so much due to what they stated. Rather, it was because one of them bore the endorsement of Rabbi Shmuel Kamenetzky, Rosh Yeshivah of Philadelphia Yeshivah, someone that Kalmanowitz considered “not fit for Torah leadership.” His campaign against my books was ultimately aimed at undermining Rabbi Kamenetzky’s reputation. Also involved in the campaign was Yaakov Kalmanowitz’s brother, Rabbi Osher Kalmanowitz of the Mir Yeshivah in New York. He did not want to openly involve himself, and so he recruited his friend Rabbi Leib Tropper of Yeshivas Kol Yaakov in Monsey.
I would add on that Kalmanovits got Leib Pinter to team up with Leib Tropper. What a pair of scoundrels.