Wikipedia: Public-sector trade union history in the US -
The first strikes by government employees took place in the 1830s, but the unions generally bypassed government employees because they were controlled mostly by the patronage system before the arrival of civil service. After the fiasco of the Boston Police Strike in 1919, which was suppressed by Governor Calvin Coolidge, and the opposition of President Franklin D. Roosevelt to labor unions in the federal government, unionization remained uncommon among government employees. Roosevelt once described that:
The Wagner Act of 1935, and subsequent legislation, applied only to employees in the private sector, since the federal government could not interfere in state government. The major exception was the emergence starting in the 1920s of unions of public school teachers in the largest cities; they formed the American Federation of Teachers (AFT). In suburbs and small cities, the National Education Association (NEA) became active, but it insisted it was not a labour union but a professional organization.
All Government employees should realize that the process of collective bargaining, as usually understood, cannot be transplanted into the public service. It has its distinct and insurmountable limitations when applied to public personnel management. The very nature and purposes of government make it impossible for administrative officials to represent fully or to bind the employer in mutual discussions with government employee organizations. The employer is the whole people, who speak by means of laws enacted by their representatives in Congress. Accordingly, administrative officials and employees alike are governed and guided, and in many instances restricted, by laws which establish policies, procedures, or rules in personnel matters. Particularly, I want to emphasize my conviction that militant tactics have no place in the functions of any organization of government employees. Upon employees in the Federal service rests the obligation to serve the whole people, whose interests and welfare require orderliness and continuity in the conduct of government activities. This obligation is paramount. Since their own services have to do with the functioning of the Government, a strike of public employees manifests nothing less than an intent on their part to prevent or obstruct the operations of Government until their demands are satisfied. Such action, looking toward the paralysis of Government by those who have sworn to support it, is unthinkable and intolerable.
Change came in the 1950s. In 1958 New York mayor Robert Wagner, Jr. issued an executive order, called "the little Wagner Act," giving city employees certain bargaining rights, and gave their unions with exclusive representation (that is, the unions alone were legally authorized to speak for all city workers, regardless of whether or some workers were members.) The first U.S. state to permit collective bargaining by public employees was Wisconsin, in 1959. Collective bargaining is now permitted in three fourths of U.S. states. By the 1960s and 1970s public-sector unions expanded rapidly to cover teachers, clerks, firemen, police, prison guards and others. In 1962, President John Kennedy issued Executive Order 10988, upgrading the status of unions of federal workers.
After 1960 public sector unions grew rapidly and secured good wages and high pensions for their members. While manufacturing and farming steadily declined, state- and local-government employment quadrupled from 4 million workers in 1950 to 12 million in 1976 and 16.6 million in 2009. Adding in the 3.7 million federal civilian employees, in 2010 8.4 million government workers were represented by unions, including 31% of federal workers, 35% of state workers and 46% of local workers. As Daniel Disalvo notes, "In today's public sector, good pay, generous benefits, and job security make possible a stable middle-class existence for nearly everyone from janitors to jailors."
In 2009 the U.S. membership of public sector unions surpassed membership of private sector unions for the first time, at 7.9m and 7.4m respectively.
In 2011 as states faced a growing fiscal crisis and the Republicans made major gains in the 2010 elections, public sector unions came under heavy attack especially in Wisconsin, as well as Indiana, New Jersey and Ohio from conservative Republican legislatures.