The Fuller Court ruled 7–2 in Adair v. United States (1908) that a federal law prohibiting railroads from discriminating against employees for union activities violated the liberty of contract found in the Fifth Amendment’s Due Process Clause and exceeded Congress’s power under the Commerce Clause because there was “no legal or logical connection” between union activities and interstate commerce.

The law prohibited an employer from threatening “any employee with loss of employment, or … unjustly discriminating] against any employee because of his membership in such a labor corporation, association, or organization.” Allegedly, William Adair, master mechanic for the Louisville & Nashville Railroad Company, discriminated against employee O. B. Coppage because of his union membership. (Adair was Coppage’s supervisor.)

The majority, in an opinion written by Justice John Marshall Harlan, reasoned that the law invaded the liberty of contract between employer and employee. Harlan reasoned that the employment setting was generally one of equality, as either employer or employees could terminate the relationship at will. Relying on this at-will employment doctrine, Harlan reasoned that just as Coppage could leave his employment at any time or for any reason, the railroad boss “was at liberty, in his discretion, to discharge Coppage from service without giving any reason for so doing.” Harlan also rejected the notion that Congress could justify this law based on its commerce powers, asking: “But what possible legal or logical connection is there between an employee’s membership in a labor organization and the carrying on of interstate commerce?”