After many long months of debate, a health care reform bill has finally passed. President Obama is expected to sign it into law this week. But as soon as that happens, another long battle is likely to begin -- in courtrooms around the country.

The Christian Science Monitor says the attorneys general of a dozen states have expressed support for taking legal action against the health care measure:

"The health care legislation Congress passed tonight is an assault against the Constitution," said South Carolina Attorney General Henry McMaster. "A legal challenge by the states appears to be the only hope of protecting the American people from this unprecedented attack on our system of government," he said in a statement.

Florida Attorney General Bill McCollum issued a similar statement late Sunday. "If the president signs this bill into law, we will file a lawsuit to protect the rights and interests of American citizens," he said.

The primary argument the states will use is that the bill violates the Constitution by requiring every American to buy insurance. Virginia also plans to challenge it on the grounds that it would violate the state's new law that says no Virginian may be compelled to purchase insurance.

But has Congress overstepped its authority under the commerce clause of the Constitution? It's hard to determine based on precedent. Georgetown Constitutional law professor Randy Barnett writes in the Washington Post:

Historically, insurance contracts were not considered commerce, which referred to trade and carriage of merchandise. That's why insurance has traditionally been regulated by states. But the Supreme Court has long allowed Congress to regulate and prohibit all sorts of "economic" activities that are not, strictly speaking, commerce. The key is that those activities substantially affect interstate commerce, and that's how the court would probably view the regulation of health insurance.

However, we may be in new territory now:

While Congress has used its taxing power to fund Social Security and Medicare, never before has it used its commerce power to mandate that an individual person engage in an economic transaction with a private company. Regulating the auto industry or paying "cash for clunkers" is one thing; making everyone buy a Chevy is quite another. Even during World War II, the federal government did not mandate that individual citizens purchase war bonds.

As much as the public might want this matter to be settled one way or another, many aspects of the health care reform measure don't take effect for 3 to 4 years. So, as they usually do, the courts may take their sweet time sorting this out.