Salanter's followers split after his death, Novardok against Slabodka, over how mussar study should be practiced. A separate and earlier controversy surrounded the movement while Salanter himself was still alive, and it was not a disagreement about method between two mussar camps but resistance from outside the movement altogether.
When Salanter began pressing, in Vilna in the 1840s, for mussar study to be given formally set aside time within the yeshiva day rather than pursued privately by individually motivated students, established rabbinic authorities in the city pushed back. Their objection was that Talmud study was the yeshiva's proper and primary work, and that time given to ethical texts, however worthy, competed with it rather than complementing it. The manner of mussar practice drew its own suspicion as well: study conducted aloud, in a plaintive singsong, sometimes to the point of tears, struck some established scholars as an emotional display out of keeping with the sober intellectual discipline the study hall was supposed to cultivate. Some communities and yeshivas restricted or resisted formal mussar study for a period as a result.
The resistance did not stop the movement, but it shaped how later mussar institutions organized themselves. When Salanter's own students later built the movement into a network of dedicated mussar houses and, afterward, an accepted place within yeshiva curricula, they were answering an objection the founder himself had already had to face down, not inventing a new complaint out of nothing.