The US Supreme Court is debating its first religious freedom case since the appointment of the new Chief Justice, John Roberts.
The group blends Christian beliefs and South American traditions
The judges are deciding whether to let a small congregation in New Mexico worship with hallucinogenic tea.
The hoasca tea is considered sacred to members of the group, O Centro Espirita Beneficiente Uniao do Vegetal.
However, the administration of President George Bush argues that it is illegal and potentially dangerous.
About 130 members of a Brazil-based church have been in long-running dispute with federal agents, who seized their tea in 1999.
Members of the group believe they can understand God only by drinking the tea, which is consumed twice a month at four-hour ceremonies.
Supreme Court justices ruled 15 years ago that US states could criminalise the use of peyote, a bitter-tasting cactus which includes the hallucinogen mescaline, by Native Americans.
But Congress changed the law to allow the sacramental use of peyote in some tribal services.
On Tuesday, Justice Sandra Day O'Connor argued with the government lawyer in his opening statement.
Ms O'Connor has resigned her place on the court but is serving until her replacement is confirmed by the Senate.
However, with Samuel Alito nominated as her replacement, she may not be still on the court to vote in the case.
In a case in 1999, Mr Alito wrote an opinion allowing Muslim police officers to keep their beards.
He also voted to permit a government holiday display which included religious as well as secular symbols, saying that it did not violate constitutional church-state separation.