This paper investigates the causal impact of the initial stage of the COVID-19 pandemic (i.e., 2020) on airlines’ crisis response strategies from the supply perspective in the EU-US market. An analytical framework examining three strategies, namely market exit, capacity retrenchment, and route hierarchy persevering, is established by utilizing the difference-in-differences (DID) method, which jointly considers dynamics in pandemic severity, border control policies, and route structure. The results demonstrate that the COVID-19 pandemic led to the disappearance of diversity in the business models of the EU-US market in the short term. Analysis of individual airlines’ capacity retrenchment strategies reveals heterogeneity in the impact of COVID-19. The route hierarchy persevering analysis exhibits three distinct strategies of airlines, i.e., connectivity-oriented, antitrust immunity joint venture-oriented, and market presence-oriented.