Objectives: To access associations between job satisfaction and supervisory support as moderated by stress. Methods: For this cross-sectional study, data collected from 591 nursing assistants in 42 nursing homes in Canada and Spain were analyzed with mixed-effects regression. Results: In both countries, stress related to residents’ behaviors was negatively associated with job satisfaction, and, in Canada, it moderated the positive association between supervisory support and job satisfaction. Stress related to family conflict issues moderated the positive association of supervisory support and job satisfaction differently in each location: in Canada, greater stress was associated with a weaker association between supervisory support and job satisfaction; in Spain, this was also observed but only when supervisory support was sufficiently weak. Discussion: Stress was associated with lower job satisfaction and moderated the association of supervisory support and job satisfaction, reinforcing the importance of supervisors supporting nursing assistants, especially during the COVID-19 pandemic.