Objective Lobbying by nonprofits is a relatively new topic that has drawn attention from political science scholars and nonprofit managers. Several studies have demonstrated there to be lobbying inequalities among nonprofits, but few have compared lobbying expenditures across groups and none have taken into account how well groups have mobilized. Methods Examining 227 groups that issue legislative “scorecards” over six terms of Congress (1999–2010), the author uses a mix of analysis of variance and regression analysis to determine whether groups with different missions lobby at different levels and whether mobilization factors, such as revenue and membership, can help explain these differences. Results The author finds that organizational revenue and membership predict how much most groups spend on lobbying. However, this finding does not apply to all groups. Public interest nonprofits lobby at higher levels as both their revenues and memberships increase. But business associations lobby at significantly high levels regardless of how well they mobilize. Conclusions These results suggest that business associations view lobbying as a more necessary activity for completion of their missions than other tax‐exempt organizations. Many of the most active groups in Washington are small business associations representing “niche” interests. If public interest groups formed around broader social interests are less represented in Washington, as these results suggest, then the voices of large sectors of society, and not just public interest group members, are lost in the policy discussion.