Today it's a penalty...tomorrow a tax?

There were quite a few interesting exchanges today during day one of the Supreme Court's hearing on the health care reform act and whether the individual mandate penalty was or was not a "tax". 

The government was boxed into a difficult position because it had to argue for purposes of the AIA that the individual mandate penalty wasn’t a tax, but tomorrow it will take the exact opposite position and say Congress passed the law under its taxing authority. Its position is further complicated by the fact that the administration still wants the court to consider the law jurisdictional, or binding on all federal courts.
At one point Breyer corrected U.S. Solicitor General Donald Verilli after Verilli had repeatedly referred to a “tax.”
“Why do you keep saying `tax’?” Breyer asked. Verrilli then referred to the “tax penalty.”
“The penalty,” Breyer insisted.
“Right, that’s right,” Verilli said.