How do religious denominations select potential adherents? Previous literature indicates that market niches direct this decision, yet few studies examine how religious groups determine their niche. Analyzing annual reports and periodicals of Reform and Conservative Jewish organizations from 1910 to 1955, I find that the two denominations responded differently to the mass influx of Jewish immigrants at the turn of the 20th century. Compared to the Conservative organization, which openly welcomed new immigrants, the Reform organization actively chose not to recruit them. Reform statements make it clear that this decision was a result of how working‐class, Eastern European immigrants threatened their American‐centered organizational identity. This finding suggests that religious institutions carefully consider their organizational identity based on nativity, ethnicity, and social class when determining whom to include in their market niche.