The U.S. Supreme Court will spend a third and final day Wednesday hearing arguments about whether the entire U.S. health care reform law should survive if a key provision is ruled unconstitutional.

Tuesday's debate focused on the so-called “individual mandate,” requiring every American to purchase health insurance or face a financial penalty. Supporters say it is needed to spread the cost of health care among all Americans, especially healthy people who might otherwise not purchase insurance, to cover more than 30 million uninsured people.

The court's most conservative members, led by Justice Antonin Scalia, expressed doubt that the government can actually require people to purchase any type of product, including health insurance.

But Scalia's liberal counterpart, Justice Stephen Breyer said the issue shows there is a “national problem that involves money, cost and insurance.”

Both Chief Justice John Roberts and Justice Anthony Kennedy also expressed concerns about the measure, but also seemed to acknowledge the need for the mandate in regulating the cost of health insurance.

The court will also spend Wednesday's session listening to arguments about the expansion of the joint federal-state health insurance program for low-income Americans, known as Medicaid, under the health care law.

The case before the nation's highest court represents a historic legal and political showdown about the Affordable Care Act, President Barack Obama's signature domestic policy. Mr. Obama signed the bill into law two years ago despite objections by opposition Republicans.

A coalition of 26 states and a group representing small businesses oppose the law, arguing that it is an overreach of the federal government's constitutional powers.

The law is the most significant reform to the U.S. health care system in four decades. It bars insurance companies from denying coverage to people with pre-existing conditions or placing a cap on the benefits available to those with serious medical conditions. Many of the law's key provisions, including the individual mandate, do not take effect until 2014.

The case comes before a divided bench made up of five justices appointed by Republican presidents and four appointed by Democrats.

The court is expected to issue its decision in June.