Sharp questioning by the Supreme Court's conservative justices has cast serious doubt on the survival of the individual insurance requirement at the heart of President Barack Obama's historic health care overhaul.
Arguments at the high court Tuesday focused on whether the insurance requirement "is a step beyond what our cases allow," in the words of Justice Anthony Kennedy.
He and Chief Justice John Roberts are emerging as the seemingly pivotal votes.
Kennedy told Solicitor General Donald Verrilli that he faced a heavy burden to justify why it was necessary to require Americans to “go into commerce” by purchasing health insurance.
Justices Antonin Scalia and Samuel Alito appeared likely to join with Justice Clarence Thomas to vote to strike down the key provision. The four Democratic appointees seemed ready to vote to uphold it.
Scalia said the mandate may be necessary, but not proper, because the federal government is supposed to have limited powers.
"If the government can do this, what else can it not do?" he asked.
There was a lot of talk about healthy young people subsidizing the health care costs of others. Justice Elena Kagan suggested they are also beneficiaries.
"The subsidizers eventually become the subsidized," she said.
Oral arguments conclude on Wednesday.
A transcription of Tuesday's proceedings:
This story has been updated.