Q. Should a well-behaved seeing-eye dog be allowed in shule?
A. Normally one may not bring an animal into a synagogue or other place of prayer. The animal may dirty the place, cause disruption to the service or affect the holiness of the moment in other ways. But Rav Moshe Feinstein noted (Ig’rot Moshe, Orach Chayyim 45) that human beings also disturb the k’dushah of the synagogue, e.g. by eating, drinking and even sleeping, all of which are forbidden. (One might add that constant moving around and talking during the service are also forbidden, and yet some supposedly Orthodox people seem to indulge in such activities despite the disruption they cause.)
Rav Moshe refers to the Jerusalem Talmud (Meg. 3:3) that states that it is permitted for a visitor to bring his mule into the synagogue, obviously provided the animal is well-behaved. Hence a blind person may bring a guide dog into the synagogue, though the animal should stay at the back of the building near the door so as not to disturb the congregation.