Democracy for America

Congress can regulate economic activity that doesn't cross state lines. There's a SCOTUS decision that came back into the news recently due to Scalia's book: Wickard v Filburn. In that case, the SCOTUS ruled that Congress could regulate economic activity that didn't leave Filburn's farm, much less cross state lines.

In addition, the large insurance firms are actually 50 smaller insurance firms. You can't sell health insurance across state lines, so even though your insurance card says "Blue Cross", it's actually "Blue Cross of California" selling the insurance if you live in CA. Someone in NY will buy their insurance from "Blue Cross of New York". So the insurance companies are NOT crossing state lines.

There has been some thought that the conservatives will use the ACA case to reverse Wickard v Filburn and similar cases in order to strike down the ACA, and since the insurance companies are not crossing state lines, they could not be regulated by the federal government.