MIAMI (Reuters)—Georgia is joining a Florida-led group of states in a lawsuit challenging President Barack Obama's overhaul of the U.S. health care system, Florida's attorney general said Tuesday.

Bill McCollum, who is seeking the Republican nomination to run for Florida governor, said a total of six U.S. states had now committed to join the original 13 that filed the lawsuit on March 23.

The suit was filed in U.S. District Court for the Northern District of Florida. It claims the reform of the $2.5 trillion U.S. health care system, pushed through by congressional Democrats after months of bitter partisan fighting, violates state government rights in the U.S. Constitution and will force massive new spending on hard-pressed states.

Legal scholars think the suit is likely to end up in the hands of the Supreme Court, but many agree that the supremacy clause of the Constitution, which puts the powers of the U.S. government above those of the states, will prevail.

"We welcome Georgia to our efforts to protect the constitutional rights of our citizens as well as the sovereignty of our states," Mr. McCollum said in a statement.

"The federal government cannot mandate that all citizens buy qualifying health care coverage or be forced to pay a tax penalty—this is unconstitutional," he said.

"We will aggressively pursue this lawsuit to the U.S. Supreme Court if necessary to prevent this unprecedented expansion of federal powers, impact upon state sovereignty, and encroachment on our freedom," said Mr. McCollum.

Mr. McCollum said last Wednesday that Arizona, Indiana, Mississippi, Nevada and North Dakota had joined in the lawsuit.

Alabama, Colorado, Idaho, Louisiana, Michigan, Nebraska, Pennsylvania, South Carolina, South Dakota, Texas, Utah and Washington had previously joined the legal challenge.

All of these states' attorneys general are Republicans, except for Louisiana and Georgia, where the post is held by Democrats.

Another state, Virginia, has filed a separate suit, arguing the new law's requirements that most Americans buy health insurance clash with a state law that exempts Virginians from federal fines to be imposed for not owning health insurance.

The Justice Department, responsible for defending U.S. law in court, has said in response to the March 23 filing that it will vigorously fight any challenges to the new health care law, which it insists is constitutional. The White House has also said it believes the suits will fail.

Mr. McCollum has said the health care reforms would add $1.6 billion to Florida's spending on the Medicaid health program for the poor.