WASHINGTON — The fate of the Affordable Care Act again hangs in the balance as the Supreme Court weighs another legal challenge to the program.

Five things to know about health care in the year ahead:

The main event

The biggest health care news of 2015 probably won’t come from Congress or the White House, but the Supreme Court. The case will be argued early in March, with a decision expected in June.

The plaintiffs contend the law as written only allows the government to subsidize coverage in states that have set up their own their own health insurance markets, or exchanges.

With Washington currently running the markets in 37 states, much of the law’s coverage expansion could unravel if the Supreme Court agrees.

It would be a moment of truth for the law’s opponents and its supporters alike.

Plan B?

If the Supreme Court rules against Obama, both sides would need a fallback plan, and quickly.

The president would have to contemplate going hat-in-hand to the Republican leadership of Congress to ask for fixes to his signature legislation, possibly opening up other contentious issues in the law.

Republican governors and state legislators would have a choice, too. They could establish insurance exchanges, or watch some constituents lose coverage.

Repeal-a-thon

With the Senate and the House both under Republican leadership, expect dozens more votes to repeal “ObamaCare.”

It’s not clear that a full repeal can get through the Senate, where Democrats retain sufficient strength to block legislation by using procedural maneuvers.

But some provisions of the law are also unpopular with significant numbers of Democrats, and bills to roll those back may emerge from Congress. Examples: a requirement that 30 hours per week counts as full time employment, a tax on medical device manufacturers, and a Medicare cost control board.

Complicated? Try taxes

Obama’s health care law uses the income tax system to deliver carrots and sticks.

The subsidies that have made premiums affordable for millions are distributed as tax credits. And the penalties imposed on those who ignore the law’s mandate to get health insurance are collected as additional taxes.

All taxpayers will have to report on their 2014 tax return whether or not they have insurance.

Those who got subsidies will have to show they got the right amount. If they received too much, their refunds will get dinged.

Those who remained uninsured will either have to pay or show they qualify for an exemption.

How many covered?

At last count, about 6.7 million people got private coverage through the insurance exchanges. Another 9.7 million got on Medicaid, the insurance program for low-income people, expanded under the law by about half the states.

Some of those people would have switched from other coverage.