Supreme Court justices will spend the next three days hearing arguments over President Barack Obama's health care overhaul.

Opponents of the law, including 26 states, believe a provision that requires individuals to get health insurance is unconstitutional. But the first arguments will concern whether a challenge to the law is premature, since the insurance requirement doesn't kick in until 2014.

A decision is expected by late June, in the midst of a presidential election campaign in which all of Obama's Republican challengers oppose the law and promise its repeal, if the high court doesn't strike it down first.