Labor unions themselves celebrated the first labor days in the United States, although there's some speculation as to exactly who came up with the idea. Most historians credit Peter McGuire, general secretary of the Brotherhood of Carpenters and Joiners and a cofounder of the American Federation of Labor, with the original idea of a day for workers to show their solidarity. Others credit Matthew Maguire, later the secretary of Local 344 of the International Association of Machinists in Paterson, N.J.