Massachusetts (defendant) sought to regulate the tobacco industry by requiring tobacco companies (plaintiffs) to give the state the ingredient lists for all tobacco products sold in the state. The tobacco companies had always treated their ingredient lists as trade secrets, and they would not disclose this information. The tobacco companies sued, claiming that requiring them to publicly disclose their ingredient lists constituted an unconstitutional taking of their trade secrets. Massachusetts argued that the regulation was necessary to promote public health. The trial court found the regulation was an unconstitutional taking because it deprived the tobacco companies of property without providing just compensation. The appeals court initially reversed the trial court, finding the regulation was not an unconstitutional taking. Then the appellate court agreed to rehear the case.