The U.S. Supreme Court handed President Barack Obama a major victory, upholding the key part of his controversial health care plan in a 5-4 decision.

The so-called “individual mandate” requires Americans to purchase heath insurance or face a financial penalty. Chief Justice John Roberts ruled with the court's more liberal justices, writing in his majority opinion that “because the Constitution permits such a tax, it is not our [the court's] role to forbid it, or to pass upon its wisdom or fairness.''

The Obama administration had argued the “individual mandate” was constitutional because all Americans will need medical care at some point in their lives — individuals do not choose to participate in the health care market.

Twenty-six states filed suit against the reform law, contending that individuals cannot be forced to buy insurance, a product they may neither want nor need.

The health care law, passed in early 2010, is the signature piece of President Obama's legislative agenda in his first term. It is intended to address rising health care costs and problems getting insurance, which have caused many Americans great financial distress.

But it was hotly fought in Congress, with members of the opposition Republican Party calling it political over-reach and saying it imposed heavy burdens on businesses.

Expected Republican presidential candidate Mitt Romney had vowed to repeal the health care law if elected in November.