In Adair v. United States, 208 U.S. 161 (1908), the Supreme Court had to deal with a question not distinguishable in principle from the one now presented. Congress, in 10 of an act of June 1, 1898, entitled "An Act concerning carriers engaged in interstate commerce and their employes" (c. 370, 30 Stat. 424, 428), had enacted "That any employer subject to the provisions of this Act and any officer, agent, or receiver of such employer who shall require any employe, or any person seeking employment, as a condition of such employment, to enter into an agreement, either written or verbal, not to become or remain a member of any labor corporation, association, or organization; or shall threaten any employe with loss of employment, or shall unjustly discriminate against any employe because of his membership in such a labor corporation, association, or organization . . . is hereby declared to be guilty of a misdemeanor, and, upon conviction thereof . . . shall be punished for each offense by a fine of not less than one hundred dollars and not more than one thousand dollars." Adair was convicted upon an indictment charging that he, as agent of a common carrier subject to the provisions of the Act, unjustly discriminated against a certain employe by discharging him from the employ of the carrier because of his membership in a labor organization. The court held that portion of the Act upon which the conviction rested to be an invasion of the personal liberty as well as of the right of property guaranteed by the Fifth Amendment, which declares that no person shall be deprived of liberty or property without due process of law. Speaking by Mr. Justice Harlan, the court said (208 U.S., p. 174): "While, as already suggested, the right of liberty and property guaranteed by the Constitution against deprivation without due process of law, is subject to such reasonable restraints as the common good or the general welfare may require, it is not within the functions of government - at least in the absence of contract between the parties - to compel any person in the course of his business and against his will to accept or retain the personal services of another, or to compel any person, against his will, to perform personal services for another. The right of a person to sell his labor upon such terms as he deems proper is, in its essence, the same as the right of the purchaser of labor to prescribe the conditions upon which he will accept such labor from the person offering to sell it. So the right of the employe to quit the service of the employer, for whatever reason, is the same as the right of the employer, for whatever reason, to dispense with the services of such employe. It was the legal right of the defendant Adair - however unwise such a course might have been - to discharge Coppage the employe in that case because of his being a member of a labor organization, as it was the legal right of Coppage, if he saw fit to do so - however unwise such a course on his part might have been - to quit the service in which he was engaged, because the defendant employed some persons who were not members of a labor organization. In all such particulars the employer and the employe have equality of right, and any legislation that disturbs that equality is an arbitrary interference with the liberty of contract which no government can legally justify in a free land."