Despite the fundamental importance of the iron and steel industry in the national economy, no significant effort to organise its workers had been made before 1918, when the American Federation of Labor set up the National Committee for the Organisation of the Iron and Steel Industry.

The campaign to organise this industry was remarkably successful; the workers, many of whom worked 12 hours a day and 7 days a week, welcomed the advent of unionism. The iron and steel companies refused to bargain with the union, however, and sacked any union members.

An industry-wide strike was called in September 1919, involving almost 370,000 workers, one of the largest strikes in U.S. history. However, the intransigence of the employers and the disunity among the strikers forced the workers to abandon the strike without winning concessions from the employers. As a result, the iron and steel industry remained an open-shop industry, for almost two decades.

Taking advantage of the weaknesses of American trade unionism, many employers acted vigorously to forestall organisation of their employees. Among other measures, they moved their establishments to areas lacking trade union traditions; abrogated existing collective bargaining agreements and refused to conclude new ones.

They also required their employees to sign so-called yellow-dog contracts binding them not to join unions and, as a means of making unionism seem less desirable, induced them to join company-controlled employee associations involving paternalistic practices, such as the establishment of health and welfare plans.

For these and other reasons, union membership dropped from the peak of 5.1 million reached in 1920 to fewer than 3.5 million in 1929. During the same period membership in company-sponsored employee associations rose from an insignificant number to about 1.5 million.

The catastrophic depression of the 1930s led to a tremendous rise in unemployment and to a corresponding further decline in union membership. Attempting to offset the adverse effects of the depression on wages and working conditions, the unions launched numerous strikes, but few were successful. The widespread use of the injunction by employers contributed to the defeats sustained by the organised labour movement.

In 1932 Congress banned yellow-dog contracts and curtailed the use of injunctions. This proved to be the forerunner of the large body of pro-labour legislation enacted after the election of Franklin D. Roosevelt to the presidency. The so-called "New Deal" was Roosevelt's program of relief, recovery, and reform that aimed at solving the economic problems created by the depression.

A series of acts helping many of the jobless over hard times, creating a system of old-age pensions and unemployment insurance, and establishing a Federal minimum wage and maximum-hours policy were enacted. Yet this new legislation excluded millions of working people and nearly 9.5 million were still unemployed in 1939.

In 1935, the U.S. Supreme Court ruled that much of the New Deal legislation was unconstitutional, causing many members of Congress to desert the president. In addition, a severe recession in 1937 led many people to turn against New Deal policies.

Thus it was that in November 1935, the leaders of eight AFL unions formed the Committee for Industrial Organisation for the purpose of conducting a unionisation campaign in the mass production industries. Among the basic manufacturing industries targeted by the CIO were iron and steel, automobile, rubber, electrical and radio, and shipping.

The CIO unions were suspended from the AFL in August 1936 and expelled in May 1938. But Congress had enacted legislation which not only reaffirmed the right of labour to organise freely and to bargain collectively, but also applied the designation "unfair" to certain practices designed by employers to impede unionisation and made those found guilty of such practices subject to penalty. One of the most significant provisions was making domination or financial support of unions by employers illegal. This virtually eliminated the company-dominated employee associations.

The campaigns to win union recognition in unorganised industries were accompanied by the greatest wave of strikes in American history. Most of the strikes were successful, and some of the largest firms in the country were prevailed upon to negotiate collective bargaining agreements.

Particularly effective in gaining its ends was the use by the CIO of the so-called sit-down strike, in which striking workers occupied the plants for the duration of the dispute. Given this combination of favourable legislation and dynamic organising drives the period at the end of the 30’s saw an unprecedented growth in union membership.