The U.S. Supreme Court heard oral arguments Tuesday in a Republican effort to strike down the Affordable Care Act health care law.
The hearing comes weeks after Justice Amy Coney Barrett joined the court, giving conservatives a 6-3 majority.
At the center of the case is a requirement in the 2010 law for most people to have a minimum level of health insurance or face a financial penalty.
In a 2012 case, the Supreme Court ruled that provision was allowed on the basis that it represented a tax that Congress is allowed to levy. In 2017, the Republican-controlled Congress and set the penalty to zero.
A group of states, led by Texas, is leading the current charge to dismantle the health care law, commonly known as Obamacare. They argue that the mandate for individuals to purchase health coverage is unconstitutional, and that without that provision, the entire Affordable Care Act must be struck down.
Part of the original congressional intent in requiring people to have coverage was that it would bring more healthy people into the system who would pay premiums without using many services, helping to offset costs of individuals who needed more care, including those with pre-existing conditions who had previously been denied coverage.
Texas and its partners argue that eliminating the individual mandate would create an imbalance and push health costs unfairly higher.
The opposition is led by California, and points to the 2017 action by Congress as evidence that lawmakers had no problem with removing only the penalty for the individual mandate while allowing the rest of the Affordable Care Act to remain in place.
They further argue that as the law stands, with no penalty in place, it merely encourages people to have health insurance, and thus cannot be seen as an unconstitutional imposition by the government.
The court is expected to issue its ruling in the case by late June or early July.
Of the justices who were members of the court during the 2012 case, Justices Samuel Alito and Clarence Thomas voted to strike down the entire law. Chief Justice John Roberts and Justices Stephen Breyer, Elena Kagan and Sonia Sotomayor voted to uphold it.
Justices Barrett, Brett Kavanaugh and Neil Gorsuch have since joined the court.
If the court strikes down the law, up to 20 million people could lose their health coverage and insurance companies could be allowed to deny coverage to people with pre-existing conditions.