Under the First Amendment, "Congress shall make no laws respecting an establishment of religion or prohibiting the free exercise thereof." Nevertheless, congressional actors have on occasion enacted laws that expressly make religion the subject of legislation. Many scholars justify these laws on the grounds that Congress at the time of the Founding had an implied power to legislate on religion if necessary and proper to an enumerated end.
Professor Lash argues that the "implied power" theory cannot withstand historical scrutiny. Whatever "implied power" arguments may have emanated from the original Constitution, those arguments were foreclosed by the adoption of the First Amendment. However, the enactment of section 5 of the Fourteenth Amendment does enable Congress to legislate- in a limited scope- on religious matters.
Kurt T. Lash, Power and the Subject of Religion, 59 Ohio St. L.J. 1069 (1998).