The emergence of American labor unions to positions of actual or potential power as organized forces in election campaigns has stirred a great deal of controversy over the limits and propriety of union political activity. A decade and more after the Taft-Hartley Act provisions on that subject, argument continues as vigorously as ever about the need for, and if a need, then the nature and extent of, legal controls over the power of union leaders to enlist and commit their membership to electioneering goals. Underlying many of these debates is the complex question of union membership solidarity in political affairs. For if, to some, solidarity suggests dangers, it also indicates difficulties in the way of making controls effective. Yet we have only begun to explore the solidarity of rank-and-file attitudes toward union political activity.