Judaism doesn't have central dogmas in the sense that some other religions do - there's no catechism or List of Things All Jews Must Believe to Be Good Jews. The closest you'd get is the Rambam's 13 principles of faith, but those are neither comprehensive nor fully agreed upon (there are other lesser known lists of fundamental principles of Jewish faith, and they don't all agree). In fact, the emphasis in the last 1500-2000 years has been on 'orthopraxy' rather than 'orthodoxy' - that is, normative practice of Judaism by following established Jewish law, rather than normative belief. As such, you can imagine that a great deal of attention has been given to the study and strict adherence to these laws, starting from the Mishnah (ca. 200 CE) forward.

This isn't to say that matters of belief, theology, and 'meta-legal' considerations aren't discussed at all in rabbinic literature. It's just that there's a subtext that while there can be a fairly large number of variants of beliefs that are often pretty set in other religions (for example, Jewish eschatology is remarkably diverse in its approach), the end state of a legal discussion will be settled one way or another. Thus, the variations in Jewish practice are remarkably small among the religious world (mostly dealing with either customs of little legal import or debates about adopting additional stringencies), but Jewish thought is much more heterogeneous.

Thus, to challenge an aspect of Jewish thought can be potentially heretical but may still be acceptable in the pale of the religious world. Yet to challenge its practice and the primacy of law - which the Mitnagdim feared Hasidic Judaism was doing - is another matter entirely. Hasidic Judaism very consciously chose to de-emphasize law in favor of a more personal, spiritual relationship with the divine. This did not sit well with the theological leaders of a religion that had only survived through careful preservation of that legal system in a lengthy and scattered diaspora.