Italian-American journalist and trade-union activist Carlo Tresca, a leading public opponent of the Mafia infiltration of unions, was assassinated in New York City.

A trade union or labor union, often simply referred to as a union, is an organization of workers whose purpose is to maintain or improve the conditions of their employment, such as attaining better wages and benefits, improving working conditions, improving safety standards, establishing complaint procedures, developing rules governing status of employees and protecting and increasing the bargaining power of workers.

Carlo Tresca was an Italian-American dissident, newspaper editor, orator, and labor organizer and activist who was a leader of the Industrial Workers of the World during the 1910s. He is remembered as a leading public opponent of fascism, Stalinism, and Mafia infiltration of the trade unions for the purposes of labor racketeering and corruption.

"Mafia", as an informal or general term, is often used to describe criminal organizations that bear a strong similarity to the original Mafia in Sicily, to the Italian-American Mafia, or to other organized crime groups from Italy. The central activity of such an organization would be the arbitration of disputes between criminals, as well as the organization and enforcement of illicit agreements between criminals through violence. Mafias often engage in secondary activities such as gambling, loan sharking, drug-trafficking, prostitution, and fraud.