The analysis seems to be somewhat simple (just rank states by union strength and COVID measures), then conclude what is reported in the title. The conclusion s

The analysis seems to be somewhat simple (just rank states by union strength and COVID measures), then conclude what is reported in the title. The conclusion seems to suffer from severe endogeneity problems as teacher unions are correlated with other factors (e.g., being on a coast) that are also correlated with COVID response. Just making the link between unions and COVID policy is naive (at best) and misleading (at worse). One thing to keep in mind when doing research in education in the US is that you have to account for its distributed structure. That is, local education agencies (usually school districts) make most of the decisions. For example, there is no California teacher contract; instead, contracts are negotiated between local teacher unions and local district. The California teacher union could have lobbied the California governor to extend school closures, but the eventual decision to how (and maybe when) to go back in person probably fell to the individual superintendents. Another example is to see what happened in Chicago Public Schools. The local union went on strike to negotiate covid-related measures. Those had nothing to do with the larger Illinois education policy. A better design for this study would have been to try to measure the strength of local unions at the district level (maybe % of membership that contributes to the political fund now that teachers can opt out from that) and try to correlate it with local COVID restrictions (like more days of teacher paid leave, mask policies, possibility of online or hybrid instruction). I suspect that there is a patchwork (read, heterogeneity) of policies that were negotiated between the union and the district that could give a better picture than what is reported in the paper. As a secondary result, you could even observe whether strong and weak unions have different preferences. Maybe strong unions prefer a safer work environment (i.e., less in person, more masks) while weaker unions prefer one-time bonuses?