The American Federation of Labor and Congress of Industrial Organizations (AFL-CIO) is a national trade union center and the largest labor union federation in the United States, formed on 4 December 1955 as a merger of the AFL and CIO unions. By 1979, the AFL-CIO had nearly 20,000,000 members, its peak strength. Nearly all unionized workers in the USA belonged to the AFL-CIO, but the rise of the Change to Win Foundation in 2005 led to the AFL-CIO losing several large unions; a number of them, such as the UFCW, would reaffiliate with AFL-CIO. In 2014, the union had 12,741,859 members.