Why did the Court treat the individual-mandate payment as a tax even though the Affordable Care Act called it a penalty?

In the 2012 case regarding the Patient Protection and Affordable Care Act, the Supreme Court addressed the individual mandate by evaluating whether it could be upheld under Congress’s constitutional powers.12

Chief Justice John Roberts rejected the government's argument that the mandate was a valid regulation of commerce, as it compelled individuals to become active in commerce rather than regulating existing activity. However, he considered the government's alternative argument: that the mandate could be construed as a tax on those who do not purchase insurance.2

Although the Affordable Care Act labeled the payment a "penalty," Roberts argued that it was functionally equivalent to a tax. Because established legal precedent requires courts to adopt any reasonable interpretation of a statute necessary to preserve its constitutionality, the Court concluded it was obligated to treat the mandate as a valid exercise of Congress’s taxing power under Article I, Section 8 of the U.S. Constitution.21