In the midst of a long article on the Wisconsin public union dispute and organized labor's role in bringing about "progressive change," Mother Jones writer Kevin Drum quotes the following statement from left-wing historian Kim Phillips-Fein:

The strength of unions in postwar America had a profound impact on all people who worked for a living, even those who did not belong to a union themselves.

This is a fairly common view among progressives, who typically see labor unions as an unalloyed force for good, and you can expect to hear many variations on it as the political battle over state budgets and public sector workers heats up. The only problem with this rosy view is that it leaves out a significant—and unpleasant—part of the story.

As scholars ranging from the liberal political scientist Ira Katznelson to the libertarian legal historian David Bernstein have now documented, organized labor's rise to power typically came at the expense of black workers. Consider collective bargaining, the legal arrangement whereby a union selected by a majority of employees receives the monopoly bargaining power to exclusively represent all employees. This valuable union tool first became part of federal law under section 7A of the National Industrial Recovery Act of 1933. Since blacks were barred from the vast majority of unions at that time, collective bargaining served as a de facto ban on all black workers in unionized shops.

Here's how an outraged 1934 editorial from the NAACP-published magazine The Crisis explained the results:

Seeking to avail itself of the powers granted under section 7A of the NRA, union labor strategy seems to be to form a union in a given plant, strike to obtain the right to bargain with the employers as the sole representative of labor, and then to close the union to black workers, effectively cutting them off from employment.

The black press reached the same negative conclusion, with leading black newspapers like The Chicago Defender attacking the pro-union NRA as the "Negro Removal Act," "Negro Run Around," and "No Roosevelt Again." According to the left-wing sociologist and historian W.E.B. Du Bois, "the most sinister power that the NRA has reinforced is the American Federation of Labor."

Two years later the Supreme Court unanimously struck down the National Industrial Recovery Act, but collective bargaining promptly reemerged via section 9 of 1935's National Labor Relations Act (also known as the Wagner Act, after its sponsor, Democratic New York Sen. Robert Wagner). That law originally contained a clause forbidding union discrimination against blacks, but the clause was dropped at the insistence of the American Federation of Labor—which then enjoyed state-sanctioned monopoly powers and continued its long tradition of excluding and mistreating black workers until the passage of federal civil rights laws in the 1960s. So much for organized labor's role in securing "progressive change."

The truth is that there's an ugly side to the "strength of unions." You may not hear much about that from liberal bloggers and noisy protesters, but it is still a fact.