2012, a presidential election year.

The issue could ultimately turn on whether forgoing medical insurance or coverage represents economic "activity," an area long considered proper for congressional oversight in interstate commerce. Opponents, including more than two dozen states, argue it is not.

The Justice Department countered that since every American will need medical care at some point in their lives, individuals do not "choose" to participate in the health care market. Federal officials cite 2008 figures of $43 billion in uncompensated costs from the millions of uninsured people who receive health services, costs that are shifted to insurance companies and passed on to consumers.

CNN poll: Majority oppose individual mandate

In the case before the 6th Circuit, four individual plaintiffs from Michigan say the government has no business interfering with their individualAffordable Care Act has about 450 components, placing a number of new or revised regulations on states, private insurance companies, employers and individuals.

Federal judges in Florida and Virginia in recent months found parts of the law unconstitutional, while colleagues in Michigan and Virginia upheld the provisions.

Federal judge tosses out health care reform act

Health care reform, a top Democratic priority since the Truman administration, was passed by the last Congress in a series of virtually party-line votes. Obama signed the act into law in March 2010. The law is widely considered to be the signature legislative accomplishment of the president's first two years in office.

Among other things, the measure was designed to help millions of uninsured and underinsured Americans receive adequate and affordable health care through a series of