To address that problem, the law's authors added the individual mandate. By requiring all adult Americans and legal residents to obtain a basic level of coverage or else pay an annual tax penalty of up to $2,085, the law seeks to deter people from signing up for insurance only after they need expensive care. It's not the only approach Congress could have taken, and it isn't perfect — the penalty seems too low to stop healthy people from going without coverage or employers from ceasing to offer health benefits to their employees. But the mandate is clearly an important component of the reforms Congress is trying to bring to the healthcare market, a means to the end of increasing coverage, improving care and slowing the growth in costs.
The Supreme Court has repeatedly held that Congress' power over interstate commerce can give it authority over activities that are local and seemingly noneconomic. For example, in 1942 it upheld farm quotas that barred wheat farmers from producing surplus grain for their own families, and in 2005 it ruled that Congress could bar Californians from growing marijuana for their own medicinal use. An important limiting factor on Congress, Justice Antonin Scalia wrote in a concurring opinion in the marijuana case, is that "such rules must be an essential part of a larger regulatory scheme" that could be undercut if the local actions in question were not regulated.