Previous research focusing on the impact of immigration on native-born workers demonstrates that workers experience wage penalties when they are employed in local occupations with a large share of immigrants. Does unionization mediate such pay penalties? Lisa Catanzarite utilizes the 2000 5% Census Public Use Microdata Sample in conjunction with pooled unionization data from the 1998-2002 Current Population Surveys to investigate the impact of union density on pay penalties in brown-collar occupations (with overrepresentations of recent-immigrant Latinos). The results indicate that unionization, particularly in the private sector, significantly eases the downward pressure on wages in brown-collar fields for both native workers and earlier-immigrant Latinos, net of individual and occupational characteristics. The analyses focus on the greater Los Angeles and San Francisco Bay Areas (California’s primary immigrant destinations) and also use data on immigrant-receiving Consolidated Metropolitan Statistical Areas nationally. The finding that union density lessens brown-collar wage penalties indicates that policies to address immigrant wage competition can be mutually beneficial to newcomers and to the more established groups with whom they may compete. Strengthening the position of marginal workers may, indeed, protect those higher in the employment hierarchy.