Prior research provides important insights into employer discrimination against mothers but has focused exclusively on college-educated mothers in professional and managerial occupations. As a result, we lack evidence about whether less-educated mothers navigating the low-wage labor market experience similar disadvantages and whether the mechanisms underlying discrimination vary across contexts. These gaps are important because more- and less-educated mothers increasingly possess distinct resources and face unique demands both at home and at work, which may impact employer perceptions of conflicts between motherhood and job performance. This study reports results from an original field experiment in which 2,210 fictitious applications were submitted to low-wage service and professional/managerial job openings across six U.S. cities, experimentally manipulating signals of motherhood status. Findings provide causal evidence that employers in both contexts discriminate against mothers relative to equally qualified childless women. However, within labor market segments, distinct job demands listed in job advertisements are associated with stronger discrimination: time pressure, collaboration, and travel in professional/managerial jobs and schedule instability in low-wage service jobs. These findings have important implications for our understanding of the mechanisms underlying mothers' disadvantages in an increasingly polarized labor market.