The coercion doctrine flows from the Spending Clause framework in South Dakota v. Dole (1987) and was elaborated in NFIB v. Sebelius (2012), where the Supreme Court ruled 7-2 that threatening to strip all Medicaid funding unless states expanded the program amounted to unconstitutional coercion. The question in the sanctuary-city airport context is whether withdrawing a federal service (CBP processing) to punish non-compliant jurisdictions operates as a coercive penalty rather than a neutral policy decision.