The União do Vegetal is the reason a great deal of the world's law on religious ayahuasca exists, because it litigated and won. In Brazil the question was settled administratively rather than judicially: federal drug regulators examined the churches in the 1980s, removed the vine from the prohibited list, and a national drug policy council resolution of January 2010 set out the terms on which religious use is permitted, naming tourism, sale and therapeutic marketing as things it does not cover.
In the United States the route was a lawsuit. Customs officers seized a shipment of the tea consigned to the church's New Mexico congregation in 1999. The church sued, arguing that the seizure burdened its exercise of religion in violation of the Religious Freedom Restoration Act, and won a preliminary injunction in the district court which survived appeal. The government took the case to the Supreme Court, which decided it in 2006 in the church's favour without a dissent, holding that the government had not carried its burden of showing a compelling interest in barring the church's sacramental use under the strict standard the Act imposes.
The decision is narrow in its terms and wide in its effect. It turns on a statute rather than on the Constitution, and it concerns one church and one substance, but it established that a small religious body could hold the government to the Act's demanding test, and it is cited well beyond the subject of ayahuasca. For the church itself the practical result is that its sessions in the United States are conducted lawfully, under an arrangement with the federal government that governs how the tea is imported and handled.