On September 4, 2014, the U.S. Court of Appeals for the D.C. Circuit took the unusual step of ordering a review of its July 22, 2014, order in the case Halbig v. Burwell, which precluded subsidies for some Americans who bought health insurance established by the Affordable Care Act. The July order would have blocked subsidies in two-thirds of the nation and, contradicted only hours later by an appellate court in Virginia, set the stage for another Supreme Court hearing on the controversial healthcare law.

At issue in Halbig v. Burwell is the wording of a crucial passage in the healthcare law that has allowed the I.R.S. to approve tax credits for people who obtain insurance through federal exchanges. As only fourteen states currently run their own exchanges the order would have blocked subsidies for millions of Americans. The critical passage approves subsidies for health policies purchased through an “exchange established by the state.” Conservative legal groups have argued for what the D.C. Circuit Court concluded in its July order: an “exchange established by the state” did not include federal exchanges.

In 2009, House Democrats favored a single nationwide federal insurance exchange, but other members of Congress disagreed. Two different Senate committees adopted health bills, one of which—the Finance Committee—wanted only state exchanges. The Health Committee’s bill also provided for the creation of state exchanges, but additionally allowed for federal exchanges in case some states refused to establish exchanges. When Congress reconciled the two bills, the language from the Finance Committee remained, allowing only for subsidies connected to an “exchange established by the state.” In 2011, after the Affordable Care Act became law, conservative opponents seized on the phrase as a basis for legal action.

Now that the D.C. Circuit has ordered an en banc review of its July decision, all thirteen D.C. Circuit judges, of which eight are Democratic appointees and five are Republican appointees, will evaluate the arguments made in Halbig v. Burwell. If the judges reverse the D.C. Circuit’s earlier decision, upholding subsidies for plans acquired through federal exchanges and concurring with the Virginian appellate court, the subsidy issue could very well be put to rest. If, however, the judges preclude the subsidies, the Supreme Court will likely once again decide the course of the healthcare law, and the meaning of five controversial words: “exchange established by the state.”