Attorneys general from at least 11 states say they will challenge the constitutionality of the healthcare reform bill passed by the House of Representatives Sunday night.

The threatened action suggests the controversial measure is about to move from the legislative realm into what could become a protracted and messy fight in the courts. The attorneys general say they will sue once President Obama signs the bill into law. They are pledging to take their battle all the way to the US Supreme Court.

“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.

Which states are moving to block healthcare law?

The comments came after a Sunday night conference call of attorneys general from 11 states, in which most expressed support for legal action to block the law. In addition to Florida and South Carolina, the attorneys general backing legal action were from Alabama, Nebraska, Texas, Pennsylvania, Washington, Utah, North Dakota, and South Dakota. [Editor's note: The original paragraph has been changed to omit a state that will not participate in legal action.]

In addition, Virginia Attorney General Ken Cuccinelli announced that he will file a lawsuit on behalf of his state challenging what he called the “unconstitutional overreach” of the healthcare law.

“Virginia is in a unique situation that allows it the standing to file such a suit since Virginia is the only state so far to pass a law protecting its citizens from a government-imposed mandate to buy health insurance,” he said. “The health care reform bill, with its insurance mandate, creates a conflict of laws between the federal government and Virginia,” Attorney General Cuccinelli said.

“Normally, such conflicts are decided in favor of the federal government, but because we believe the federal law is unconstitutional, Virginia’s law should prevail.”

Attorneys general and other opponents of the bill had threatened legal challenges for months. Most recently, they objected to the proposed “deem and pass” legislative maneuver that had been the suggested route to passage of the bill. But congressional leaders jettisoned the maneuver on Saturday and relied instead on traditional up or down votes on Sunday. That decision eliminated potential grounds for a lawsuit.

Has Congress overstepped its authority?

At the center of the controversy is the bill's inclusion of a federal mandate requiring all Americans to purchase health insurance or face penalties. Opponents say this measure stretches Congress’s constitutional power to “regulate commerce … among the several states” beyond any meaningful limits on federal authority. They say Congress is authorized to regulate behavior to protect public safety or welfare, but federal lawmakers overstep the constitutional limits of their power when they begin ordering Americans to purchase certain products.

“With this law, the federal government will force citizens to buy health insurance, claiming it has the authority to do so because of its power to regulate interstate commerce,” Cuccinelli said. “We contend that if a person decides not to buy health insurance, that person – by definition – is not engaging in commerce, and therefore, is not subject to a federal mandate.”

The Virginia attorney general added: “Just being alive is not interstate commerce. If it were, there would be no limit to the US Constitution’s commerce clause and to Congress’s authority to regulate everything we do.”

In addition to challenging the individual mandate to buy health insurance, opponents had threatened to sue to block favorable concessions to the states of Nebraska and Louisiana that were designed to entice senators from those states to vote in favor of the healthcare bill.

[Editor's note: The original headline of this story has been changed to correct the number of states ready to challenge the healthcare reform legislation.]