Another big decision looms for the Affordable Care Act this summer and, while a negative outcome may not torpedo the president’s signature legislation, it could severely hamper it. Debate in the case in point, King v. Burwell, will start before the Supreme Court on March 4. The arguments will concern whether the legislation allows for tax credits to low- and moderate-income individuals in states that aren’t running their own insurance exchanges. Here’s a brief rundown of the case and what’s at stake:

Who’s involved?

King v. Burwell is a consolidation of three cases, all asserting that language in the ACA only allows for subsidies in state-run health insurance exchanges, and not those deployed by the federal government.

Who’s affected?

Millions of members in as many as 37 states — mostly red ones — using insurance marketplaces that are either facilitated, supported or in partnership with the federal government, according to the National Institute for Health Care Management.

What would they lose?

A ruling in favor of the plaintiffs, removing subsidies for low-income individuals, would reduce enrollment by some 9.6 million or 70 percent, according to a recent study by the RAND Corp. Unsubsidized premiums, meanwhile, would increase 47 percent, or about $1,610 annually, for a nonsmoker who bought a Silver-level marketplace plan. The uncompensated care burden also likely would increase for hospitals.

The end of the ACA?

A decision in favor of the plaintiffs isn’t enough to completely sink Obamacare; it would only take out one of the law’s three legs — the others being the individual mandate and the marketplaces, notes Timothy Jost, a professor of law at the Washington and Lee University School of Law. What it would amount to, he believes, is basically that health reform would occur mostly in blue states. But a group of hospitals including the American Hospital Association said that such a scenario would be a “disaster” for millions of Americans, according to a friend-of-the-court brief.

What’s the timeline?

Jost says that with the oral arguments starting in early March, a final decision likely would come in late June or early July.