The Musical Mutual Protective Union (MMPU) was a New York union of musicians, formed in 1863, with a focus on payment made to musicians in theaters and at balls.In 1885, the union was open to “all instrumental performers, who have been residents of the United States for the period of six months previous to application.” Foreign musicians were not allowed to play in orchestras unless they were in a union.The union become Local 301 of the American Federation of Musicians in 1902.