Objective. The COVID-19 pandemic led to widespread school closures affecting millions of K-12 students in the United States in the spring of 2020. Groups representing teachers have pushed to reopen public schools virtually in the fall because of concerns about the health risks associated with reopening in person. In theory, stronger teachers' unions may more successfully influence public school districts to reopen without in-person instruction. Methods. We examine the relationship between teachers' union strength and the reopening decisions of 835 public school districts in the United States using regression analyses. Results. We find that school districts in locations with stronger teachers' unions are less likely to reopen in person even after we control semiparametrically for differences in local demographic characteristics. These results are robust to four measures of union strength, various potential confounding characteristics, a further disaggregation to the county level, and various analytic techniques and datasets. We do not find evidence that measures of COVID-19 risk are correlated with school reopening decisions. Conclusion. Our findings that school closures are uncorrelated with the actual incidence of the virus, but are rather strongly associated with unionization, implies that the decision to close schools has been a political-not scientific-decision.School reopening-when and how to do it-has become one of the largest and most politicized policy deliberations amid the coronavirus pandemic. At least 55 million students from over 120,000 public and private schools have been affected by closures since March 2020. 1 While only time will tell the ramifications that the absence of in-person learning will have on students' human capital development, a large body of literature suggests that higher academic achievement is associated with improved life outcomes (e.g., Chetty, Friedman, and Rockoff, 2014;Hanushek, 2011). However, Gross and Opalka (2020) found that only about one-third of the 477 public school districts operating remotely in their analysis required teachers to deliver remote instruction, as opposed to no instruction, in the spring of 2020. They also found that less than half of the districts expected teachers to take attendance or check in with students regularly.School closures have had an even more immediate effect on the U.S. labor market. Because roughly 32 percent of households have children under the age of 14 living with them, coupled with the collapse in the childcare market (Ali, Herbst, and Makridis, 2021), the inability to reopen schools will necessarily affect the ability for the United States to fully reopen its labor market and attain traditional levels of full-time employment since many parents will be unable to return to work.