To study whether dairy workers in California have lower baseline and greater cross-shift decrements in lung function than control employees. A cross-sectional study of 210 dairy and 47 control workers who completed questionnaires and spirometry before and after the work shift. Dairy work was associated with mean baseline differences of -0.132 L (P = 0.07) and -0.131 L (P = 0.13) in forced expiratory volume in 1 second and forced vital capacity, respectively, compared with control employees, adjusting for age, height, smoking status, and days back at work since last day off. Dairy work was associated with a mean cross-shift difference of -65.2 mL (P = 0.02) and -103.1 mL (P < 0.01) in forced expiratory volume in 1 second and forced vital capacity, respectively, adjusting for smoking status and work-shift time. Dairy work in California was associated with mild acute airway obstruction. The unclear long-term effect of dairy work in California merits further investigation.