Check out the National Labor Relations Act (NLRA) for the legal basis for the right to form a union: http://en.wikipedia.org/wiki/National_Labor_Relations_Act . The NLRA not only protects the right of workers to organize, but explicity states that they should.
As Mangus said certain groups of workers like farmworkers are excluded from the NLRA. This means that if such workers democratically vote to have a union represent them and negotiate a collective bargaining agreement, the employer has no legal obligation to recognize the union and negotiate. Several farmworker unions have overcome this obstacle by pressuring companies and growers through boycotts and corporate campaigns to recognize the union and negotiate a contract. Two main examples of this are the United Farm Workers and the Farm Labor Organizing Committee www.floc.com . Both Unions currently represent thousands of farmworkers in different states around the country.
Many people, especially on the right, subscribe to the ideas that Mangus expounds upon above, claiming that markets are the only efficient decision making mechanism and that organizing is unnecessary interference. Some go on to claim unions are parasitic entities that prey on hard working folks. I oftentimes have a hard time sorting out the people who actually believe this from the people who promulgate such ideas based on their position in owner and managerial classes of society. They want the societal balance of power unchallenged.
Interestingly, when the elections come around some on the populist right (think Lou Dobbs) are fond of bemoaning the loss of American jobs and the talk of the hard life of working people. Rather than talking of the decline of union density in almost every industry across the board the simple scapegoat used is “immigrants.” Historically, union density (the percentage of a certain industry that is unionized) decline correlates pretty closely with the decline in the size and stability of the middle class in the US. Organized workers bring up the standards of all workers in an industry, organized or not. This decline in union density is directly tied to a concerted effort to push back labor laws and the perfection by the modern corporation of the anti-union campaign (the Reagan years were horrible). The reality of out-sourcing, however, musn’t be ignored as a factor.
To be fair, it must be pointed out that many in the labor movement have resorted to the blame the immigrants card; it has long been a debate in the labor movement of whether to shut them out or organize them. More and more though, people in the labor movement are realizing that in an increasing global economy, unions need to be more global-minded and work in solidarity with workers and unions from around the world.
You will not find me defending union actions blindly, but I will defend fiercely the need for Unions. There is a history of corruption, discrimination, and authoritarianism in the labor movement. Just like any human organization, from a company to a government, these things are bound to happen. The key is membership involvement and systems of democratic accountability. All around the country unionized workers enjoy more of a voice on their job and wages and benefits that provide a little security in a sometimes turbulent global economy.
Side note: best union movies ever to see:
1. “Salt of the Earth.” banned in the US when first released because of the red scare, a profound treatment of race class and gender in a historically based film about latino and white miners in NM.
2.On the documentary side, check out the engaging “Harlan County, USA.” A sometimes violent miners strike. Highly recommended.