Technically, there is no conversion required for the vast majority of Orthodox Jews who might want to be accepted into a Reform congregation. If an Orthodox Jew shows up in a Reform congregation and takes part in a service, they will be counted as fully Jewish without question. The great difficulties come when Reform Jews get interested in Orthodox Judaism, because Reform accepts as Jews people who are not considered as Jews by the Orthodox -- The Orthodox to not recognize the legitimacy of Reform conversions nor do they recognize as Jews those who claim Jewish status through patrilineal descent.(OK, there is one difficult class where Reform Jews might ask for conversion. The child of a Jewish mother and a non-Jewish father who grew up in a non-religious household would be welcome as a Jew