returning to their workplace, it may turn out that letters directed at employees will be more effective than what was found in this experiment, particularly given the increased relevance and importance of social protection in worker welfare. Unlike other studies evaluating the impacts of tax experiments, ours was unable to assess the success of the letter delivery (both for employers and employees), which is problematic since letters might have been delivered at a time when the intended audiences were not present. This would suggest that our impact estimates are likely a lower bound estimate of the true effect of the letters.

Second, businesses managed their payroll more actively than usual during the pandemic. Firms responded to the crisis by letting go of employees or reducing work hours or pay – and then re-hiring as lockdowns were lifted and business activity started recovering. This meant that payroll was a more significant concern – and fewer firms just submitted a standard automated payroll declaration. This may have led to a stronger than usual response of payroll declarations to the employer letters - though it may also have reduced persistence of payroll treatment effects.

Third, in a crisis context, enforcement messages (which were relatively muted compared to the literature) may have been less effective than they would be in more normal times, while appeals to social solidarity may have been relatively more effective. In a context in which businesses are struggling to make ends meet in the face of the pandemic, threatening messages enforcing tax collection may not have appeared credible and may have in fact hardened the resolve of businesses not to cooperate with the government. Moreover, the language in the strong letter was relatively tame, in the sense that enforcement actions to be carried out in the face of noncompliance were abstract, not referring to many actions beyond monitoring of behavior (the same was true of original letters used by the GDT in past campaigns). For example, in a study in Poland summarized by Hernandez et al. (2017), enforcement toned language was much more concrete, and thus potentially more credible (e.g., referring to Enforcement Orders and freezing of salaries and bank accounts). In contrast, given a national tragedy, businesses may have been particularly receptive to messages appealing to their social duty to contribute to revenue mobilization to fight the pandemic.

Fourth, given the role of the tax authority in delivering wage subsidies during the early stages of the pandemic, its communications may have had greater than usual weight in terms of influencing business declaration behavior, and for some types of firms more than others. Notably, during the lockdowns in the initial phase of the pandemic, the tax authority was responsible for administering wage subsidies paid out on basis of the declared payroll of businesses. This meant that letters sent out by the tax authorities were possibly read more carefully than in normal times, particularly for businesses that were disproportionately impacted by the pandemic (e.g., professional services compared to wholesale and retail trade, where we saw some heterogeneity in impacts, discussed earlier). Finally, the crisis has likely increased noise in the tax data, making it more difficult to identify a statistically significant impact of the letters on payroll declaration behavior. For all these reasons, further research is needed to fully determine how contextdependent the results of the RCT presented in this study are.

# VI. Discussion

This study provides a unique opportunity to evaluate the impact of strategic notifications to taxpayers in the context of a global pandemic. Letters were delivered at a time when businesses were forced to drastically cut their operations and likely downsize (both in terms of employees and production overall), and business (and thus accounting) practices likely shifted dramatically. This may have led to a stronger than usual response of payroll declarations to the soft-toned employer letters (and weaker than usual reaction to enforcement messages, which could have been viewed as non-credible or insensitive) particularly since tax 18