Hull also questioned whether other parts of the law could solve some of the health care problems addressed by the individual mandate.
Katyal reacted sharply by saying it would be a "deep, deep" mistake to say that some of the problems could be solved through other mechanisms in the law.
Former Acting Solicitor General Walter Dellinger, who attended the arguments and believes the law is constitutional, said Wednesday's panel of judges asked "more skeptical questions of each side and, perhaps, asked more skeptical questions of the government" than a panel of judges who heard a similar case in Virginia. The panel in that case was comprised of three judges who were nominated to the bench by Democratic presidents and they seemed openly skeptical of the arguments of those challenging the health care law.
Judge Dubina was appointed by President George H.W. Bush, while Hull and Marcus were both Clinton nominees.
The arguments also marked the first time an appellate court has heard a challenge to another provision of the law that expands the reach of Medicaid.
Clement argued that the government had gone too far in asking the states to add significant administrative expenses and force them to eventually cover more citizens through Medicaid.
According to the law, the federal government will initially fund 100 percent of the expanded benefits. State participation in the program has always been voluntary.
Judge Dubina seemed receptive to Clement's argument.
Elizabethe Wydra, the chief counsel of the Constitutional Accountability Center who filed a brief in defense of the law, noted that this is the third appellate court to hear arguments.
"Many of the judges, whether considered to be conservative or liberal, recognize that the decision not to buy health insurance is, in fact, an economic decision," she said. "Supreme Court precedent makes clear that Congress has authority to regulate such economic activity."
But Florida's attorney general, Pam Bondi , who attended the arguments and is opposed to the law, said afterwards, "The federal government could not rebut our argument that the individual mandate is an unprecedented intrusion on individual liberty.
The issue is expected ultimately to reach the Supreme Court.