A labor union is an association of workers in a particular trade, industry, or plant, which uses collective action to press for improvements in the pay, benefits, and working conditions of its members. The roots of trade unionism as a movement can be traced to 18th-century Britain, where the first fraternal and self-help associations of workingmen were established. During the 19th century, trade unionism developed simultaneously in America, Great Britain, and other parts of Europe.

When unions became outspoken on political and economic matters, they generally met with hostility from employers and government. They were often prosecuted under restraint-of-trade and conspiracy statutes. Consequently, workingmen's associations in Britain and the United States were usually fleeting enterprises through much of 19th century. Overall, British unionism exhibited a stronger inclination to political activity than its American counterpart, culminating in the formation of the Labour Party in 1906.

In 1886 several unions of skilled workers established the American Federation of Labor (AFL), which marked the start of a large-scale labor movement in the U.S.  Unionism in America gained political legitimacy more gradually than in Britain, by a series of court decisions that incrementally placed greater restrictions on the use of injunctions and conspiracy laws against unions.

According to author Jonah Goldberg:

"Traditional, private sector unions were born out of an often bloody adversarial relationship between labor and management. It's been said that during World War I, U.S. soldiers had better odds of surviving on the front lines than miners did in West Virginia coal mines. Mine disasters were frequent; hazardous conditions were the norm. In 1907, the Monongah mine explosion claimed the lives of 362 West Virginia miners. Day-to-day life often resembled serfdom, with management controlling vast swaths of the miners' lives. And before unionization and many New Deal-era reforms, Washington had little power to reform conditions by legislation."

Government unions, by contrast, have no such narrative in their history. Public-sector workers were already earning good salaries in 1962 when President Kennedy issued an executive order lifting the federal ban on government unions. Thanks to civil service regulations and similar laws, government workers had enjoyed good working conditions for generations.

The earliest unions in both the U.S. and Great Britain consisted of skilled workers, as it was widely believed that unskilled laborers were not suited for union organization. But over time, in Britain and elsewhere in Europe, unions for unskilled or semi-skilled workers grew into viable entities. This trend eventually came to America as well, when, in 1935, the AFL expelled a small group of member unions that were attempting to organize unskilled laborers. The expelled unions joined forces to form the Congress of Industrial Organizations (CIO), which successfully organized the steel and automobile industries.

During the latter years of the Depression, the U.S. labor movement was infiltrated by members of the Communist Party. Soon after World War II, however, unions generally began a process of purging their ranks of Communist influences. That process was given particular urgency in 1947 when Congress passed the Taft-Hartley Labor Act, which stipulated that unions would be required to file financial reports and affidavits affirming that none of their officers were Communists.

From the 1950s through the mid-1990s, union leadership tended generally to be politically centrist. This trend was personified by such figures as Albert Shanker, who served as president of the American Federation of Teachers (AFT) from 1974 to 1997; George Meany, who led the AFL-CIO from 1955 to 1979; and Lane Kirkland, who succeeded Meany as AFL-CIO president from 1979 to 1995. When Shanker and Kirkland's respective tenures ended in the 1990s, however, they were replaced by leftists like Sandra Feldman (AFT), and John Sweeney (AFL-CIO). These individuals, along with other leftist ideologues at the helm of powerful unions, quickly transformed the labor movement into a “progressive” crusade.

Another major figure in the labor movement was Andrew Stern, the former New Leftist who served as president of the Service Employees International Union (SEIU) from 1996 to 2010. As Ryan Lizza, associate editor of The New Republic, notes, today’s SEIU leaders "tend to be radical, even socialist."

The leftward ideological shift of the unions brought with it a dramatic increase in political activism by union leaders and foot soldiers alike. In 1996, for instance, Andrew Stern told SEIU officials that he expected “every leader at every level of this union, from the international president to the rank-and-file member, to devote five working days this year to political action” in support of the Democratic Party and its candidates. Meanwhile, another major union, the National Education Association (NEA), has assembled a permanent, paid, full-time staff of at least 1,800 United Service (UniServ) employees who function as political operatives -- more than the Republican and Democratic Parties combined. Beyond this, leftwing unions like the SEIU and NEA contribute huge sums of money to Democratic candidates during every election season.

Government (public-sector) unions have become major players in the American political process, providing a strong base of support for the left. As of 2010, fully 36.2 percent of government employees were unionized. This is virtually the only sector of American society where unions have been growing. In the mid-20th century, nearly half of private-sector workers were union members. By 2010, that proportion had plummeted to a mere 6.9 percent of private-sector workers.

One reason for this decline is that unionized private-sector companies, forced to pay wages higher than the law of supply-and-demand warranted, became uncompetitive in the global marketplace and went out of business.

Public-sector unions, by contrast, have suffered no such consequences because their success depends upon their ability to siphon up taxpayer dollars, rather than upon their fiscal responsibility and the realities of the market. Public employees earn approximately 45 percent more, on average, in wages and benefits than comparable private-sector workers. In addition, public employees, as compared to their private-sector counterparts, pay less for their health care and receive pensions that are far more generous -- often without contributing any of their own money to those benefits. Rather, American taxpayers foot the bill.

The Capital Research Center points out that public-sector unions invariably support government provision of health care "not only because it would shift health care costs from unionized employers to taxpayers, but because greater government involvement in the one-sixth of the American economy that is health care would create opportunities to mandate union representation."

Because government workers get their money not from a free marketplace but from taxes, their unions have a large incentive to advocate on behalf of political leaders who support higher taxes and bigger government, which can, in turn, produce an ever-greater number of public-sector union jobs. Indeed, when California voters approved Proposition 13 in 1978, cutting the state's astronomical property taxes by 57 percent, the public-sector unions were enraged. Union leader Ron Coleman said, "We're not going to just lie back and take it."

As pollster Scott Rasmussen explained in the Wall Street Journal, “Public-sector workers want government to grow first, and the overall health of the economy isn’t as relevant to them.” This mindset translates into overwhelming public-sector union support for Democratic politicians who will block efforts to reduce government and to lower taxes. Indeed, public-sector union money constitutes the lifeblood of the Democratic Party.

Union political support for Democrats is a trend that has been in place for decades, and it shows no signs of abating. In 2010, America's top 20 labor unions gave more than $68 million in campaign contributions to federal candidates -- with 94 percent of the total going to Democrats and just 4 percent to Republicans. Most of the total -- 88 percent -- came from political action committees (PACs) associated with those 20 unions, and the remaining 12 percent came from individual union members. A similar trend can be seen in state and local political campaigns. Fifteen unions gave at least $1 million to Democrats during the 2008 and 2010 campaigns. Combined, their donations totaled more than $206 million, of which fully 91 percent went to Democrats.

Below is a list of all the labor unions that ranked -- along with various corporations, special-interest groups, and professional associations -- among the 140 leading donors to U.S. political parties and their candidates from 1989-2010. Every one of these unions, without exception, gave the vast majority of its donations to Democrats. Next to each union's name is the total dollar amount of its political contributions during the two-decade period, as well as what percentage of that money went to Democrats:

• AFSCME: $43,337,561 (98%)
• International Brotherhood of Electrical Workers: $32,930,966 (97%)
• National Education Association: $32,021,910 (93%)
• Laborers Union: $30,106,550 (92%)
• Carpenters & Joiners Union: $29,154,808 (89%)
• Service Employees International Union: $29,139,982 (95%)
• Teamsters Union: $29,126,809 (93%)
• American Federation of Teachers: $28,731,591 (98%)
• Communications Workers of America: $28,273,156 (98%)
• United Auto Workers: $26,949,252 (98%)
• Machinists & Aerospace Workers Union: $26,170,977 (98%)
• United Food & Commercial Workers Union: $25,226,733 (98%)
• AFL-CIO: $18,744,496 (95%)
• Sheet Metal Workers Union: $17,901,313 (97%)
• Plumbers & Pipefitters Union: $17,547,376 (94%)
• Operating Engineers Union: $17,103,385 (85%)
• United Steelworkers: $14,493,901 (99%)
• United Transportation Union: $14,414,260 (88%)
• Ironworkers Union: $14,069,875 (92%)
• American Postal Workers Union: $13,312,673 (95%)
• Seafarers International Union: $8,704,594 (85%)
• Transport Workers Union: $8,582,649 (95%)
• Amalgamated Transit Union: $7,648,918 (93%)

In 1996, Rutgers economics professor Leo Troy estimated that in each election cycle at that time, union political expenditures totaled approximately $500 million. In 2004, the National Institute for Labor Relations Research placed the figure at $925 million. According to the Center for Responsive Politics, eight of the top ten all-time political contributors are labor unions.

The money that is transferred in these political contributions derives from the dues which are automatically taken out of the paychecks of millions of union members. As NEA general counsel Robert Chanin candidly said at the NEA's annual meeting in July 2009:

"Despite what some among us would like to believe, [the NEA is effective] not because of our creative ideas. It is not because of the merit of our positions. It is not because we care about children and it is not because we have a vision of a great public school for every child. NEA and its affiliates are effective advocates because we have power.

“And we have power because there are more than 3.2 million people who are willing to pay us hundreds of millions of dollars in dues each year, because they believe that we are the unions that can most effectively represent them, the unions that can protect their rights and advance their interests as education employees.”

Contrary to Chanin's assertion, however, many NEA members are not happy about paying their union dues. According to a 2004 Zogby poll, 63 percent of all employees, and 61 percent of unionized workers, said that union members should not be required to contribute their dues to political causes they opposed. Moreover, a McLaughlin & Associates poll found that two-thirds of union workers were unaware of their right to withhold dues whose use was explicitly slated for political purposes.

In early 2011, Florida legislators passed HB1021, a bill banning automatic paycheck deductions for state-employee union dues, and allowing union members to decide whether or not they want their dues to be used for political advocacy by union leaders.

Also in contradiction to union-official claims, polls have consistently shown that a majority of employees do not want to join labor unions. For example, in a March 2007 Opinion Research Corporation poll, 64 percent of workers said they would prefer their present jobs to remain non-union. An August 2006 Zogby poll found that 58.2 percent of employees were either “definitely against” or “probably against” joining a union. Only one-third of respondents said they would actually lean toward joining a union, and scarcely a third of those said they were "definitely" in favor of doing so.

The frequency with which union officials commit crimes against their own members is noteworthy. In recent years, hundreds of union officials have been indicted for Labor Management and Reporting Disclosure Act violations, including embezzlement, falsification of reports and records, destruction of records, extortionate picketing, and deprivation of rights by violence. The Office of Labor-Management Standards (OLMS) notes:

"In fiscal year 2005, OLMS completed 325 criminal cases. Indictments increased to 114, a 16 percent increase from FY 2001. The number of convictions dropped to 97. In addition, in FY 2005 court-ordered restitution amounted to $23,244,979."

In addition, the Department of Labor's Office of Inspector General reports that between 2001 and 2005, some 1,142 racketeering indictments were issued against labor unions, resulting in 705 convictions and more than $400 million in fines and restitution. Nearly half of these racketeering investigations involved pensions and employee welfare benefit plans.

A 2004 Zogby International poll found that 71 percent of union members said the government should do more to protect them from corrupt union officials, and that unions should be required to provide detailed reports of their finances in order to discourage abuses. According to the U.S. Department of Labor Office of Inspector General, “Schemes involving bribery, extortion, deprivation of union rights by violence, and embezzlement used by early racketeers are still employed to abuse the power of unions.”

Trevor Loudon, former vice president of ACT New Zealand -- a political party that promotes free-market classical liberalism in the New Zealand Parliament -- writes that "[t]he U.S labor movement is now completely dominated by socialists and communists." In March 2011, Loudon reported that 96 union leaders and activists from 26 states had recently gathered for an "Emergency Labor Meeting" in Cleveland to “explore together what we can do to mount a more militant and robust fight-back campaign to defend the interests of working people.” This closed-door meeting was endorsed by many of the most radical socialist labor leaders in America, including affiliates of such groups as the Committees of Correspondence for Democracy and Socialism, the Democratic Socialists of America, the Communist Party USA, the Party for Socialism and Liberation, the Socialist Party USA, and the International Socialist Organization.

The RESOURCES column on the right side of this page contains a link to the section where profiles of labor unions can be found. It also contains links to articles, essays, books, and videos that explore, in depth:

• the agendas, activities, and immense political influence of labor unions in the United States;
• the Employee Free Choice Act, proposed legislation that would not only increase the power of America’s labor unions, but would also give the federal government the power to dictate the terms of many private-sector contracts;
• how the teachers' unions have failed black and Hispanic students in particular; and
• the labor-union movement's alliance with certain elements of the religious left.