Emerson Jackson, a Native American Church holyman, performs a cedar ceremony outside the Supreme Court in 1989. (AP Photo/Rick Bowmer) Many have attacked Indiana's "religious freedom law" as an invitation to discriminate against gay people, but Gov. Mike Pence says it simply mirrors a federal law passed in 1993.

That year, Congress enacted the Religious Freedom Restoration Act as a liberal response to an unusual Supreme Court case concerning Native Americans' right to smoke peyote, an activity closely tied to their religious beliefs.

In Employment Division v. Smith, two Native Americans in Oregon, who worked as counselors at a drug rehab facility, ingested peyote, a small cactus known to contain mescaline, a powerful hallucinogen. The Native American Church, also known as Peyotism or Peyote Religion, promotes smoking peyote for medicinal and spiritual purposes.

After finding out about the counselors' habit, the organization soon fired them. Naturally, they applied for unemployment benefits. But Oregon's unemployment office denied their claim because "misconduct" caused their dismissal.

Fighting for their benefits, the two Native American employees sued the state, claiming they used the drug for religious purposes and denying their benefits violated the First Amendment's free exercise clause.

While the employees lost at the state level, the US Supreme Court eventually heard the case. In 1990, the justices ruled 6-to-3 against the Native Americans, finding an individual's religious affiliation did not exclude him or her from complying with valid laws.

Writing for the majority, Justice Antonin Scalia noted that permitting exceptions to state laws for religious purposes would be a slippery slope, potentially allowing people to sidestep taxes or required vaccinations.

Peyote contains mescaline, a psychoactive drug used to hallucinate. Wikimedia Commons Three years later, however, Congress responded to the court's decision with the Religious Freedom Restoration Act, which required the government "not substantially burden religious exercise without compelling justification."

The act restored the precedence of a 1963 Supreme Court decision, Sherbert v. Verner, which found that South Carolina didn't have a "compelling" interest in denying unemployment benefits to a Seventh-day Adventist Church woman who refused to work on Saturday, the Sabbath day of her faith.

Individual states soon passed their own laws to create religious exemptions. Despite the outrage over Indiana's law, 40% of states have similar provisions on their books.

In a statement, Sen. Charles E. Schumer (D-N.Y.) explained the difference between the federal and state laws: The federal law only applies when people sue the government for violating their freedom of religion, while the broader state laws can affect lawsuits against individuals. Businesses could use the logic behind state religious freedom laws to deny service based on religious principles, according to Schumer's explanation.

And we've already seen the latter application of a state religious freedom law. An Indiana pizza parlor run by a Christian family, one of the first business to employ the state's new law, vowed to never deliver to a gay wedding.

Since nationwide backlash against Pence and his law, the governor has sought to clarify that it doesn't allow discrimination, and Indiana has proposed to offer special protections to gays and lesbians.