Data on state household incomes released yesterday by the U.S. Census Bureau illustrate once again just how critical unions are in building a strong middle class, as states with greater union membership continued to have more robust middle classes than those with lower union membership in 2012.

Maintaining a strong and vibrant middle class is essential for all states, as prosperous middle-class households are among the most powerful drivers of economic growth and among the most critical contributors to economic mobility.

Labor unions strengthen the middle class by advocating for workers’ interests both in the workplace and in the political arena. By fighting for fair wages and basic benefits, as well as defending programs such as Social Security and the minimum wage, organized labor helps promote upward mobility for all workers and ensures that our democracy works for the middle class. As today’s data make clear, unions fulfill this essential role not only at the national level but at the state level as well.

This fact becomes readily apparent when comparing the strengths of middle classes in states with higher and lower unionization rates in 2012. To measure this strength, we look at the percentage of aggregate state income taken home by the middle 60 percent of households last year—essentially, the share of a state’s economic pie that went to families in the middle class. Of the five states with the lowest unionization rates in 2012—North Carolina, Arkansas, South Carolina, Mississippi, and Georgia—all had middle classes of below-average strength. On the other end of the spectrum, four of the top five union states—Alaska, Hawaii, Washington, and Rhode Island—had middle classes of above-average strength.

Further illustrating this divide is the gap between the average percent of total state income going to the middle class in the top 10 and bottom 10 most-unionized states. In the top 10 most-unionized states, households in the middle class received 47.4 percent of total state income on average; in the bottom 10 states, households in the middle class received only 46.8 percent. While a difference of 0.6 percentage points may not initially appear large, in 2012, 0.6 percent of Pennsylvania’s aggregate income, for example, would have equaled over $2 billion, or almost $700 per middle-class household.

Together, these figures illustrate once again just how tangible of an impact organized labor has on the everyday lives of middle-class families. When the middle class does well, so does the American economy. But to rebuild both, we must ensure that unions are strong enough to fight for middle-class interests in the workplace and in the political arena.

David Madland is Director of the American Worker Project at the Center for American Progress Action Fund. Keith Miller is a Research Assistant with the American Worker Project.