By David Savage

The Supreme Court will decide the fate of President Obama's health care law yet again, this time ruling on whether low- and middle-income Americans may receive subsidies in two-thirds of the states to make insurance more affordable.

Currently, about 5 million Americans have subsidized insurance they bought through a health care exchange, or online marketplace, run by the federal government.

The conservative group that has brought the case now before the high court argues that such an arrangement is illegal. They maintain that the Affordable Care Act, as written, allows the government to subsidize health insurance only in the states that have set up their own insurance exchanges.

Thirty-six states have not set up their own exchanges, relying instead on the marketplace run by the federal government. If the challenge to the law succeeds, residents of those states would be unable to obtain subsidies unless the states involved change their positions.

Administration lawyers and the Democratic lawmakers who sponsored the law have called the argument absurd. They say the law intended to provide insurance subsidies nationwide, regardless of whether it was bought through a federal or state exchange.

The language in the law saying subsidies may be paid through an "exchange established by the state" needs to be read in the context of the entire statute, they argue.

A federal appeals court based in Virginia agreed with the administration's position, but now the high court has decided to review that ruling, putting a central element of the law back into jeopardy. Two years ago, the high court by a 5-4 vote upheld the Affordable Care Act as constitutional. The new case will determine whether the law can work as its sponsors intended. Friday's announcement that the court would consider the case came as a surprise. Many legal experts had predicted that the justices would take no action for now because a challenge to the insurance subsides is still pending before the U.S. Court of Appeals for the District of Columbia.

The fact that the court decided to go ahead and hear the appeal of the Virginia decision without waiting for the D.C. appeals court to rule indicates that at least four of the conservative justices remain determined to knock down the Affordable Care Act.

The court does not reveal how many justices vote to hear a case, but its rules require at least four.

Two years ago, Chief Justice John G. Roberts Jr. broke from the conservative bloc and cast the deciding vote to preserve the federal health care law. Four justices _ Anthony M. Kennedy, Antonin Scalia, Clarence Thomas and Samuel A. Alito Jr. _ dissented and said the law should be struck down in total.

The conservative advocates who brought the next round of lawsuits had their sights set on those justices. They hope that this time they will win over Roberts to gain a majority.

The case, called King vs. Burwell, is to be argued early next year and decided by June.