Aggressive behavior against out-group members often rises during periods of economic hardship and health pandemics. Here, we test the widespread concern that the Covid-19 crisis may fuel hostility against people from other nations or ethnic minorities. Using a controlled money-burning task, we elicited hostile behavior among a nationally representative sample (n=2,186) in the Czech Republic, at a time when the entire population was under lockdown. We provide causal evidence that exogenously elevating salience of the Covid-19 crisis magnifies hostility against foreigners. This behavioral response is similar across various demographic sub-groups. The results underscore the importance of not inflaming anti-foreigner sentiments and suggest that efforts to restore international trade and cooperation will need to address both social and economic damage.