From "The UAW's Awakening" in today's Wall Street Journal: "The problem with unions is not all that dissimilar to that posed by entrenched management: Once they win comfortable contracts, they often become impediments to the kind of innovation and flexibility essential to success in today's economy. So in the name of "job security," they undermine a company's -- or a nation's -- competitiveness. The result, over time, is less job security for everyone, especially the union workforce. There's no better example of this than GM, where the UAW now represents about 74,000 hourly workers, compared to 246,000 in 1994. Some security."
This is classic textbook economics, paraphrased from Gwartney and Stroup:
For a time, unionized workers enjoy higher wages and job security. In the long run, however, investment will move away from firms with low profitability (Ford and GM). To the extent that the profits of unionized firms are lower (GM, Ford), investment expenditures will flow into the nonunion sector (Toyota, Honda, Nissan) and away from unionized firms. As a result, the growth of both productivity and employment, as well as market share, will tend to lag in the unionzed sector.
The larger the wage premium of unionized firms and the greater the guarantees of job stability, the greater the incentive to shift production toward nonunion operations. Empirical evidence shows that industries and companies with the largest union wage premiums and greatest guarantees of job stability are precisely the industries and companies with the largest declines in the employment of unionized workers.
Bottom Line: Gains in the short run of higher-than-market wages and benefits, and greater job security, eventually undermine the companies employing unionized workers, destroying hundreds of thousands of union jobs in the long run. The more success a union has in the short-run, the greater the failure in the long run. The discipline of the market eventually dominates and prevails.