A federal appellate court in Atlanta raised red flags for the administration's signature health reform law Wednesday, questioning the government's ability to require people to buy health insurance.

Wednesday's hearing was the third time in the past two months that federal appellate courts have considered a constitutional challenge to the health care law. It is arguably the highest profile case, with 26 states challenging the federal law. The case is widely expected to reach the Supreme Court.

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According to the AP, the judges expressed unease over the law's health insurance requirement. Chief Judge Joel Dubina, nominated by President George H.W. Bush, asked, "If we uphold the individual mandate in this case, are there any limits on congressional power?" Circuit Judges Frank Hull and Stanley Marcus, both appointed by President Clinton, asked similar questions later on.

Other questions from the three-judge panel signaled trouble for the administration.

The judges focused on the question of whether the court could rule separately on the insurance mandate. That question is only relevant if the court finds the mandate unconstitutional.

"One argument that could be of some concern to United States is the extent to which judges on the panel asked about severability," said former Solicitor General Walter Dellinger, who served in the Clinton administration and attended the arguments.

The judges also pushed aside questions on plaintiffs' ability to challenge the law in court. According to Dellinger, Dubina said the individual plaintiffs had standing to challenge the insurance requirement, while the states had standing to challenge the law's required Medicaid expansion.