The development of organized labor in the United States has created difficult legal and social problems with which the courts and the legislatures are required to deal. The courts were the first to deal with these problems and, rightly or wrongly, attempted to apply to them the existing rules of law. For instance, the rules of property law have been applied. Where organized labor interfered with the carrying of the mail, it was said that the federal government had a property right in the mails. Where the carrying on of a business was interfered with, it was held that the right to conduct a lawful business was property. The practice of the courts in trying to settle the labor problems by calling different interests, especially those of the employer, "property" interests with which organized labor cannot legally interfere has been severely criticized. Also the courts have applied the laws of nuisance. Where organized labor interfered with the interests of the neutral public, a public nuisance was found which could be enjoined. The doctrine of Lumley v. Gye, prohibiting the inducement of breach of contract, has been applied very effectively where a so-called "yellow dog'' contract exists between the employer and his employees. The rules prohibiting unfair competition and intimidation have been freely applied. In dealing with the constitutionality of the state anti-injunction statutes, it is important that these general rules followed by courts of equity in granting labor injunctions, in the absence of statute, be kept in mind.