South Carolina Attorney General Henry McMaster says he and Florida Attorney General Bill McCollum will file a federal lawsuit challenging whether the bill is constitutional.
McMaster says that when the national government and Congress "start going wild," the states have to rein them in.
The U.S. House plans to vote on the plan Sunday. McMaster and McCollum, both Republicans, will argue that it violates state sovereignty because it requires that all Americans have some form of health insurance.
They expect other attorneys general will sign onto their lawsuit as well.
Democratic critics call such lawsuits frivolous.