The U.S. Supreme Court has decided to hear an appeal of a key provision in President Barack Obama's health care law.

The nation's highest court said Monday it will consider legal arguments about whether most Americans should be required to buy health care insurance, or pay a fine if they fail to do so. A hearing on its constitutionality is likely early next year, with a decision by the end of June, in the midst of the U.S. presidential campaign.

The requirement is part of a sweeping reform of the national health care system approved by Congress and signed into law by President Obama more than a year ago. But the mandate that individuals purchase insurance — rather than being allowed to wait until they are sick to buy it — has proved to be the law's most controversial provision.

The law is an important domestic legislative achievement for President Obama, but all of the Republican presidential contenders seeking to replace him say they want to repeal it. The White House said it is pleased the court is considering the law's legitimacy and confident that the court will rule that it is constitutional.

There have been numerous challenges to the mandate. Some lower courts have upheld it while one declared it unconstitutional, ruling that Congress overstepped its authority in mandating the purchase of insurance.

At the heart of the legal debate is what the U.S. government can compel its citizens to do as part of regulating economic activity in the country. Opponents of the law have raised questions about what other products Americans could be forced to buy if the insurance requirement is ruled legal.

Supporters of the law say the insurance purchase is needed to spread the cost of health care among all Americans. They say that if people waited to buy insurance until they needed help paying for their health care, insurance premiums for others would be unaffordable.