The Religious Freedom Restoration Act of 1993, Pub. L. No. 103-141, 107 Stat. 1488 (November 16, 1993), codified at 42 U.S.C. § 2000bb through 42 U.S.C. § 2000bb-4 (also known as RFRA), is a 1993 United States federal law that "ensures that interests in religious freedom are protected." The bill was introduced by Congressman Chuck Schumer (D-NY) on March 11, 1993. A companion bill was introduced in the Senate by Ted Kennedy (D-MA) the same day. A unanimous U.S. House and a nearly unanimous U.S. Senate—three senators voted against passage—passed the bill, and President Bill Clinton signed it into law.
RFRA was held unconstitutional by the United States Supreme Court, as applied to the states in the City of Boerne v. Flores decision in 1997, which ruled that the RFRA is not a proper exercise of Congress's enforcement power. However, it continues to be applied to the federal government—for instance, in Gonzales v. O Centro Espirita Beneficente Uniao do Vegetal and Burwell v. Hobby Lobby Stores, Inc.—because Congress has broad authority to carve out exemptions from federal laws and regulations that it itself has authorized. In response to City of Boerne v. Flores and other related RFR issues, twenty individual states have passed State Religious Freedom Restoration Acts that apply to state governments and local municipalities.
This summary is from Wikipedia.