In its first religious freedom decision under Chief Justice John Roberts, the court said the government cannot hinder religious practices without proof of a "compelling" need to do so.
"This is a very important decision for minority religious freedom in this country," said lawyer John Boyd, who represents about 130 U.S. members of O Centro Espirita Beneficiente Uniao do Vegetal who live in New Mexico, California and Colorado.
The tea, which contains an illegal drug known as DMT, is considered sacred to members of the sect, which has a blend of Christian beliefs and South American traditions. Members believe they can understand God only by drinking the tea, which is consumed twice a month at four-hour ceremonies.
A trial judge found the government's evidence that the drug is harmful was equal in weight to information provided by the sect that said its method of use in tea is not.
Roberts, in writing the opinion for the court, said the government had failed to prove that federal drug laws should outweigh the Religious Freedom Restoration Act, which Congress passed in 1993 to prohibit burdening a person's exercise of religion.
The Bush administration had argued that the drug in the tea not only violates a federal narcotics law but a treaty in which the United States promised to block the importation of drugs including dimethyltryptamine, also known as DMT.
Religious groups of various faiths, along with civil liberties organizations, filed friend-of-the-court briefs supporting the sect. "This is just one step in the right direction in the fight for religious liberty," said Jared Leland, legal counsel for The Becket Fund for Religious Liberty in Washington.
New Justice Samuel Alito did not take part in the case, which was argued last fall before Justice Sandra Day O'Connor's retirement. Alito was on the bench for the first time on Tuesday.
The justices sent the case back to a federal appeals court, which could consider more evidence.
Roberts, writing his second opinion since joining the court, said that religious freedom cases can be difficult "but Congress has determined that courts should strike sensible balances."
The case is Gonzales v. O Centro Espirita Beneficiente Uniao Do Vegetal, 04-1084.