Here's the full attorneys general suit filed by Tom Corbett and others -- in a 22-page pdf -- to block health care reform. It's mostly a constitutional argument. The main thrust is the following:

2. The Act represents an unprecedented encroachment on the liberty of
individuals living in the Plaintiffs’ respective states, by mandating that all citizens and legal residents of the United States have qualifying healthcare coverage or pay a tax penalty. The Constitution nowhere authorizes the United States to mandate, either directly or under threat of penalty, that all citizens and legal residents have qualifying healthcare coverage. By imposing such a mandate, the Act exceeds the powers of the United States under Article I of the Constitution and violates the Tenth Amendment to the Constitution.

3. In addition, the tax penalty required under the Act, which must be paid by
uninsured citizens and residents, constitutes an unlawful capitation or direct tax, in
violation of Article I, sections 2 and 9 of the Constitution of the United States.

4. The Act also represents an unprecedented encroachment on the sovereignty of the states. For example, it requires

that Florida vastly broaden its Medicaid eligibility standards to accommodate upwards of 50 percent more enrollees, many of whom must enroll or face a tax penalty under the Act, and imposes onerous new operating rules that Florida must follow. . . . 

5. Further, the Act converts what had been a voluntary federal-state partnership into a compulsory top-down federal program in which the discretion of the
Plaintiffs and their sister states is removed, in derogation of the core constitutional
principle of federalism upon which this Nation was founded. In so doing, the Act
exceeds the powers of the United States and violates the Tenth Amendment to the
Constitution.

6. The Act contains several unfunded mandates that will cost state
governments significantly.