The Customs Service and the Drug Enforcement Administration say ayahuasca is illegal because it contains dimethyltryptamine (DMT), which is banned by the Controlled Substances Act. Uniao do Vegetal members say their use of ayahuasca is protected by the Religious Freedom Restoration Act (RFRA), which prohibits the government from imposing a "substantial burden" on the free exercise of religion unless it is "the least restrictive means of furthering [a] compelling governmental interest."You'll notice that when the federal government passed a law allowing drug use the Court managed to rediscover the Interstate Commerce Clause.In 2002 a federal judge, concluding that Uniao do Vegetal was likely to win this argument, issued a preliminary injunction barring the government from interfering with the church's rites. A three-judge panel of the U.S. Court of Appeals for the 10th Circuit upheld the injunction in 2003, and last year the full appeals court concurred.
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Congress passed RFRA with the intent of restoring the "compelling interest" test the Court had applied before the peyote case. Although the Court ruled in 1997 that RFRA was unconstitutional as applied to the states, it still binds the federal government.