Attorneys general and governors for 20 states won’t be alone in their legal challenge to President Barack Obama’s health care overhaul.

The nation’s most influential small business lobby is going to court with them.

The National Federation of Independent Business will join the argument that Americans cannot be required under the Constitution to obtain insurance coverage, the group’s president, Dan Danner, said Friday.

“This law is the first time the federal government has required individuals to purchase something simply because they are alive,” said Mr. Danner.

Regardless of whether that argument sways federal judges hearing the case, NFIB’S involvement ensures the point will be heard extensively during the fall political campaigns. With 350,000…