Why did Republican-led states challenge the Affordable Care Act in federal court?

Republican-led states challenged the Patient Protection and Affordable Care Act (PPACA) in federal court primarily on two constitutional grounds:12

• Commerce Clause: Plaintiffs argued that the individual mandate—which required most Americans to obtain health insurance—exceeded Congress’s power under the commerce clause. They contended that the mandate regulated "inactivity" (the failure to purchase insurance) rather than active interstate commerce.12
• Spending Clause and Coercion: States alleged that the expansion of Medicaid imposed an onerous financial burden. They argued that the federal government’s conditions for receiving matching funds were so coercive that they violated the spending clause of the U.S. Constitution, effectively forcing states to participate in the expansion against their will.12

These legal challenges reflected broader concerns among opponents regarding the expansion of federal power under the administration of President Barack Obama.2