At first glance, public-sector labor unions are just one of many types of organizations that participate in the political process. However, these unions differ significantly from other interest groups made up of individual citizens or non-labor organizations. Because their members' interests are tied to government policy, these unions are more focused and vigilant in their drive to influence policy than other groups are. And they have immense financial resources to deploy: in 25 U.S. states, laws guarantee unions both members and revenue. As a result, public-sector unions bring vast resources to their political activities at the federal, state, and local levels. Public-sector unions also differ from most interest groups in their allegiance to a single party and a single agenda in debates about the role of government. They are focused on a few key issues relating to the government jobs of their members: more government employment and thus higher taxes and more government services. A number of states are currently struggling with controversies over public-sector unions' impact at the bargaining table on matters such as health-care costs, pensions, performance pay, and worker flexibility. But unions may have more impact on public policy--and the costs of government--through their uniquely powerful tools for electioneering and lobbying. Today's debates should expand their focus from collective-bargaining issues to take into account these facts about public-sector unions as political actors. (Contains 8 charts, 1 table and 28 endnotes.)