A three-judge panel on the US Court of Appeals for the Fifth Circuit heard oral arguments Tuesday in a case that asks whether, because of the new tax law, the Affordable Care Act (ACA) no longer qualifies as a tax, rendering the individual mandate upheld by the US Supreme Court in 2012 no longer valid.

In December a judge for the US District Court for the Northern District of Texas ruled that when the Tax Cuts and Jobs Act of 2017 reduced the ACA’s shared-responsibility payment for not obtaining health insurance to $0, the provision ceased being a tax, making it an invalid exercise of Congress’ power to tax.

The lawsuit was filed by 20 Republican attorneys general and governors and two individuals, Neill Hurley and John Nantz. Defendants are the US, the Department of Health and Human Services and its secretary Alex Azar, the IRS and David Kautter in his capacity as its Acting Commissioner. The states of California, Connecticut, Delaware, Hawaii, Illinois, Kentucky, Massachusetts, Minnesota, New Jersey, New York, North Carolina, Oregon, Rhode Island, Vermont, Virginia and Washington, and the District of Columbia also intervened as defendants. Following the filing of the suit, the Trump administration said it would not defend the ACA.

On June 26 the Fifth Circuit asked the parties to respond to three questions concerning standing ahead of oral arguments. Much of Tuesday’s questioning continued this inquiry, including whether it is possible to apply a ruling only to the states identified as plaintiffs in the complaint.