May I attend a social event at a Reform temple?
“Chased by a would-be assassin and a snake ready to strike, the victim passes a house of heresy,” conjectures the Gemara, ”may he enter?"
Halachah clearly forbids a Jew to enter a beis avodah zarah (house of idol-worship) or minim (heretics). We keep a general distance of four amos (arm-lengths, about six feet) from the place of worship and should not even pass through the courtyard of the building. “Harchek me’aleha darkecha” (distance your path from it), the passuk in Mishlei warns.
Yet in circumstances of sakanah (mortal danger) many issurim (prohibitions) are suspended. When in danger, the Gemara states, better enter a beis avodah zarah than one occupied by minim—for idol-worshippers reject He whom they don’t know, but heretics knowingly deny Him.
Contemporary poskim discuss whether establishments that do not ascribe to the tenet of Torah min HaShamayim (the Divine origin of the Torah—e.g. religious institutions of the Reform and Conservative movements) are similar to idolatrous temples—or perhaps even worse—houses of heresy. In addition to the obvious issur of davening there (or even answering Amen to their prayers), it is forbidden to enter during the prayer service for any reason. This is on account of the restriction of mar’is ayin (appearance of wrongdoing) since observers may assume that the person is entering to worship. As well, a religious Jew associating with such a place may be considered abetting wrongdoers or lending a form of legitimacy to their movement—but all these apply primarily to being in the sanctuary, especially during services.
If a kosher event is being held in a social hall that is separate from the place of prayer during a time that is not set aside for prayer, there is some room for heter (leniency) b’sha'as hadechak (in pressing circumstances) when without recourse—and with Rabbinic guidance. But there are those who still strictly avoid entering even another part of the building, ever, on account of the severity associated with a temple as a house of avodah zarah or of minim, as outlined in the Gemara.