The Supreme Court heard arguments Wednesday in the latest major challenge to President Barack Obama's health care reform, but the justices were expectantly divided along ideological lines on the issue.

The meeting was held to determine whether the Affordable Care Act renders people from all 50 states eligible for federal tax subsidies to lower the cost of insurance premiums, or if the law limits tax credits only to those who live in states that created their own insurance marketplaces, according to The Associated Press.

If the Supreme Court rules to limit where subsidies are available, independent studies estimate that some 8 million people could lose insurance coverage because their states decided to opt against their own marketplace, AP said. All over one very specific four word clause tucked away in the health care law.

The justices aggressively questioned lawyers representing both sides - the Obama administration and the health law challengers. But one justice in particular - Chief Justice John Roberts, who surprised many in 2012 when he voted to uphold the law - hardly said a thing, in what some say was a concerted attempt to remain impartial.

"Roberts, who's usually a very active participant in oral arguments, said almost nothing for an hour and a half," said CNN's Supreme Court analyst Jeffrey Toobin, who attended the hearing. "[Roberts] was so much a focus of attention because of his vote in the first Obamacare case in 2012 that he somehow didn't want to give people a preview of how he was thinking in this case ... he barely said a word."

Michael Carvin, the lawyer challenging the Obama administration's interpretation of the law, argued it was clear that Congress authorized subsidies for middle and low income citizens living only in states with exchanges "established by the states," which is only 16 states. Millions of Americans living in the other 34 states are still receiving federal subsidies, though.

The Obama administration, on the other hand, argues that the law provides subsidies for all 50 states.

Justice Ruth Bader Ginsburg said she believes the law allows the states to be flexible in how they participate in the health care program, adding that giving subsidies only to people in some states would be "disastrous," according to AP.

Justice Elena Kagan suggested the law should be interpreted in its "whole context" rather than the one, four word snippet at the heart of the debate. Justice Sonia Sotomayor agreed - saying it was like hiding "a huge thing in a mousetrap" - as did Ginsburg, who said the words were buried and "not in the body of the legislation where you would expect to find them."

Questions posed by Justice Anthony Kennedy, who is often a key swing vote, didn't make clear how he will vote, as he critically questioned both sides.

When Obama's legal representative, Solicitor General Donald Verrilli, stepped up to the lectern, the liberal justices backed down, and Justices Samuel Alito and Antonin Scalia fired off a round of tough questions, according to Fox News.

Verrilli criticized the challengers, saying their argument "revokes the promise of affordable care for millions of Americans - that cannot be the statute that Congress intended."

But Justice Antonin Scalia immediately challenged his statement, saying, "It may not mean the statute they intended, the question is whether it's the statute they wrote."

Justice Clarence Thomas remained quiet throughout, CNN noted, and Justice Samuel Alito questioned Verrilli's argument, wondering why states that were caught off guard by the subsidies didn't sign amicus briefs.

A decision in the case is expected by late June.