A new dataset of organizational testimony at U.S. Congressional hearings on environmental protection is used to examine how social movement organizations use issue expertise to gain access to the policy process. Environmental movement organizations (EMOs) are shown to testify in greater numbers at hearings that consider proposed legislation, compared to hearings that are exploratory or investigatory in nature. The increased representation at legislative hearings is unique to EMOs; other kinds of organizations do not obtain similar increases in legislative access. These findings suggest that, due to their scientific expertise and perceived legitimacy, EMOs receive privileged access to the policy process relative to other organizations affected by environmental policy and at a later stage than has been proposed by prior work examining social movement access to the policy process.