South By North Strategies, Ltd.

From the Center on Economic and Policy Research’s analysis of union membership trends in 2009:

The collapse of the housing bubble and corresponding decrease in private consumption and investment partially reversed small but significant membership gains by the labor movement over 2007 and 2008. As total employment in 2009 fell by several million workers, unions lost more than 770,000 members. Steep declines in manufacturing and construction accounted for nearly 60 percent of the reduction in private-sector employment over 2009. In turn, more than 60 percent of the union membership loss occurred within those two industries.
…
As a result, the union membership rate in the private sector, the bulk of the U.S. economy, dropped to 7.2 percent in 2009 from 7.6 percent in 2008. The fall in private sector unionization in 2009 was largely due to regional variation in the recession’s burden on industries. In the manufacturing industry, for instance, the union membership rate fell from 11.4 percent in 2008 to 10.9 percent in 2009. This decline in the national rate stemmed largely from the disproportionate impact of the recession on manufacturing jobs in the Midwest, where unions are relatively strong.