(Reuters) - The U.S. Supreme Court will consider on Wednesday a second major legal attack on President Barack Obama's healthcare law, with conservative challengers taking aim at a pivotal part of the statute that authorizes tax subsidies to help people afford insurance.
The court is set for a one-hour oral argument starting just after 10 a.m. (1500 GMT), with a ruling on the fate of Obama's signature domestic policy achievement due by the end of June.
On a chilly, damp, cloudy day in the U.S. capital, about a couple hundred demonstrators mostly from pro-Obamacare forces including labor unions, a nurses group, Planned Parenthood and women's groups gathered on the sidewalk in front of the white marble columned courthouse ahead of the argument.
Some chanted, "Healthcare under attack, stand up, fight back." Some of the signs said "Don't take my care" and "8 + million could lose coverage."
More than 100 people also lined up in order to get seats inside the courtroom to hear the arguments. U.S. conservatives have denounced the law as a government overreach, but the law's opponents were not seen in large numbers outside the courthouse.
If the court rules against the Obama administration, up to 7.5 million people in at least 34 states would lose the subsidies that help low- and moderate-income people buy private health insurance, according to the consulting firm Avalere Health.
The Democratic-backed Affordable Care Act, narrowly passed by Congress in 2010 over unified Republican opposition, aimed to help millions of Americans who lacked any health insurance afford coverage.
The case does not affect people who obtain health insurance through their employer.
The legal question, hinging on just a few words in the expansive law, is whether only people who have bought insurance on state exchanges qualify for the tax-credit subsidies.
Thirteen states and the District of Columbia have set up such exchanges, with another 34 run by the federal government and three operating as state-federal hybrids.
The first time Obamacare came before the nine justices three years ago, the court was split 5-4. Chief Justice John Roberts, a conservative appointed by President George W. Bush, was the key swing vote, siding with the court's four liberals to uphold the law on constitutional grounds.
Roberts and fellow conservative Justice Anthony Kennedy are the most likely swing votes in the new case.
The court will be focusing on whether a four-word phrase in the law has been correctly interpreted by the administration to allow subsidies to be available nationwide.
That provision says subsidies are available to those buying insurance on exchanges "established by the state." The challengers, financed by a libertarian Washington group called the Competitive Enterprise Institute, say the government should lose based on the plain meaning of that phrase.
The case is King v. Burwell, U.S. Supreme Court, No. 14-114.
(Additional reporting by Lisa Lambert; Editing by Will Dunham)
