The Free Exercise Clause

As stated in the Free Exercise Clause of the First Amendment, 
"Congress shall make no law ... prohibiting the free exercise [of religion]"

The Free Exercise Clause

• prohibits government from interfering with individuals' right to exercise religion freely
• uses the term "no law," though the government has occasionally imposed limits (i.e. human sacrifices)
• implies that while the freedom to believe is absolute, the ability to act on those freedoms may not be

http://www.firstamendmentschools.org/freedom/faq.aspx?id=12923