Since the start of the COVID-19 pandemic, nursing home residents have accounted for roughly one of every six COVID-19 deaths in the United States. Nursing homes have also been very dangerous places for workers, with more than one million nursing home workers testing positive for COVID-19 as of April 2022. Labor unions may play an important role in improving workplace safety, with potential benefits for both nursing home workers and residents. We examined whether unions for nursing home staff were associated with lower resident COVID-19 mortality rates and worker COVID-19 infection rates compared with rates in nonunion nursing homes, using proprietary data on nursing home–level union status from the Service Employees International Union for all forty-eight continental US states from June 8, 2020, through March 21, 2021. Using negative binomial regression and adjusting for potential confounders, we found that unions were associated with 10.8 percent lower resident COVID-19 mortality rates, as well as 6.8 percent lower worker COVID-19 infection rates. Substantive results were similar, although sometimes smaller and less precisely estimated, in sensitivity analyses.