Buried deep inside Princeton University political scientist Martin Gilens’ research highlighting the excessive influence the rich have on modern U.S. politics, there is a hidden gem exploring which interest groups best represent the priorities of the middle class. Gilens found that, while most powerful interest groups advocate for policies that predominately benefit their narrowly defined members, relatively few focus on policies that the middle class supports. According to Gilens, most of these middle-class oriented groups are unions, which is a big problem for the United States, as unions have been declining in membership and losing power for decades.

Gilens determined how closely the positions taken by leading interest groups matched up with the preferences of the middle class by measuring the correlations between the policy preferences of Americans at the 10th, 50th, and 90th income percentiles—as recorded in more than 1,000 poll questions—and the public stances of powerful interest groups on these particular questions. Groups were selected from Fortune magazine’s “Power 25,” lists of the most powerful interest groups in Washington during the Clinton and George W. Bush administrations, in addition to the 10 industries with the highest lobbying expenditures. The chart below illustrates Gilens’ key findings. The groups listed at the top tend to share the policy preferences of Americans earning near the 50th percentile, which we define as the middle class, while the groups at the bottom consistently take positions that conflict with the preferences of the middle class. Our figure only includes interest groups where the correlations with middle-class positions were highly statistically significant, but it is worth noting that most of the groups not shown also tended to take positions opposed by the middle class.

What is striking about Gilens’ findings is that all five of the unions studied—the AFL-CIO, the American Federation of State, County, and Municipal Employees, the International Brotherhood of Teamsters, the United Automobile Workers, and the National Education Association, or NEA—and a few other groups, such as AARP, the National Governors Association, or NGA, and the collective advocacy efforts of universities, are among the only groups that more often than not lobby for policies the middle class supports. Many leading interest groups, such as the U.S. Chamber of Commerce, oil companies, and other business organizations, actively advocate against policies that the typical American favors. All in all, of the 40 groups Gilens presented analysis for, only 8 strongly supported the interests of the middle class.

Similarly, the policy positions of these interest groups tend to align with the preferences of the poor, defined as Americans at the 10th income percentile. AARP, universities, the NGA, and unions advocate for policies the poor support, while most prominent interest groups—typically organizations representing business owners—work against the preferences of the poor. Interestingly, most unions, AARP, universities, and the NGA also tend to support policy measures favored by people with incomes at the 90th percentile, though the correlations are not as strong as those with the middle class and the poor and are sometimes statistically insignificant. This suggests that unions, AARP, universities, and the NGA tend to support policy measures that most Americans want, while most interest groups—especially those representing business owners—tend to represent the views of a very narrow constituency.

The efforts of unions and other groups that represent the interests of the middle class and the poor are critical for making democracy work. Few individuals have the time or resources for sustained engagement with the political system, especially among the poor and middle class. Interest groups provide the structure for individuals to pool their resources on behalf of their preferred policies, provide legal and regulatory expertise, and ensure effective implementation of policies—working not only to help pass legislation but also lobbying for implementation once policies have been passed. They also can mobilize members, and often the general public, at key points throughout the legislative process.

Democracy suffers when the most influential interest groups only represent the views of a narrow group of citizens, such as business owners or other rich and powerful people, while overlooking the preferences of the larger middle class. In order for democracy to work for the middle class, interest groups representing the wealthy need to be offset by a counterbalancing force. Indeed, President James Madison, a chief framer of the U.S. Constitution, recognized that interest groups representing all perspectives—not just those of the rich—were necessary for our system of government to function properly. In President Madison’s essay “Federalist No. 10,” he cautioned that “the most common and durable source of factions has been the various and unequal distribution of property.” President Madison’s solution to the problem of factions was to ensure that all interests were able to participate in the democratic process in order to provide a check on the other, writing that with “a greater variety of parties and interests; you make it less probable that a majority of the whole will have a common motive to invade the rights of other citizens.” But when one interest or faction isn’t represented, or is only weakly represented, the checks and balances of the system fail and some interests dominate at the expense of others.

Of the organizations that represent middle-class interests, unions are arguably the most important. While universities and the NGA often advocate for policies aligned with middle-class interests, they generally take positions on a relatively small amount of the policy areas Gilens reviewed. Unions, on the other hand, engage in a large number of issue areas that benefit the middle class, supporting policies such as raising the minimum wage, increasing health care coverage, and promoting retirement security. AARP is another important group, especially when it comes to giving a voice to the needs of older Americans. Unions, however, represent broad swaths of industries and workers and warrant particular attention, as they comprised five of the eight groups Gilens identified with positions that most reflect middle-class interests.

Given that unions have lost power in recent decades—in part because conservatives have been waging a war against them—it is unsurprising that the middle class has not fared well over this period of time. Indeed, the weakening of labor unions strongly correlates with the shrinking of the middle class: As union membership declined, the share of national income for the middle 60 percent of households has fallen to record lows. Harvard University Professor Bruce Western and University of Washington Professor Jake Rosenfeld found that union decline explains one-fifth to one-third of the growth in inequality in the United States over recent decades.

With the increasing influence of interest groups, especially those that represent the narrow interests of the wealthy, the counterweight unions provide in advocating for middle-class interests is even more crucial. If the middle class is to regain its policymaking voice and economic strength, reinvigorated unions will be critical in the fight for their interests. Any agenda to rebuild the middle class needs to include a plan to strengthen unions and empower the workers they represent.

David Madland is the Director of the American Worker Project at the Center for American Progress Action Fund. Danielle Corley is a Special Assistant for the Economic Policy team.