Adair v. United States, 208 U.S. 161 (1908), was a US labor law case of the United States Supreme Court which declared that bans on "yellow-dog" contracts (that forbade workers from joining labor unions) were unconstitutional. The decision reaffirmed the doctrine of freedom of contract which was first recognized by the Court in Allgeyer v. Louisiana (1897). For this reason, Adair is often seen as defining what has come to be known as the Lochner era, a period in American legal history in which the Supreme Court tended to invalidate legislation aimed at regulating business.