Understanding the determinants of worker effort is central, as even small changes in productivity can have significant implications for economic growth and labor market performance. This study examines the relationship between extreme temperatures and work effort—proxied by non-work time while at the workplace—using the ATUS 2003–2019. Results indicate that extremely hot days (? 100ºF) are related to increased time spent at work not working, particularly among women in non-supervised occupations. On these days, women in non-supervised occupations spend 6.79 more minutes at work not working compared to comfortable temperature days. Men, by contrast, do not exhibit significant changes in non-work time at work. Furthermore, the results align with increased worker bargaining power during economic expansions, which facilitates labor supply adjustments on extremely hot days, and with hypotheses regarding adaptation and acclimation to high temperatures in warmer counties. These findings underscore the relevance of temperature as a determinant of worker effort, reveal a previously overlooked margin of labor adjustment, and highlight the moderating role of occupational supervision in shaping behavioral responses to environmental stressors.