This case involves Alfred Smith and Galen Black, two members of the Native American Church in Oregon. These two men also happened to work as counselors at a private drug rehabilitation clinic in that state. Perhaps unsurprisingly, the two men were fired after a drug test showed that they had ingested peyote. When the two men filed for unemployment, Oregon denied their benefits on the grounds that they had been dismissed for work-related misconduct. The men alleged that this decision was unlawful, since the men had been fired for ingesting peyote as part of a religious exercise.
The Supreme Court, in an opinion authored by Justice Antonin Scalia, ruled that the State may enact “neutral law[s] of general applicability” which are not required to make exceptions to enforcement for persons on account of their religious beliefs. Essentially, since Oregon was not trying to suppress people’s religious beliefs, the Court worried that creating an exception in this case would result in every citizen “becom[ing] a law unto himself.”
Read more about Employment Division v. Smith (1990) here.