In his ruling, Vinson criticized Democrats for seeking to have it both ways when it comes to defending the mandate to buy insurance. During the legislative debate, Republicans chastised the proposal as a new tax on the middle class. Obama defended the payment as a penalty and not a tax, but the Justice Department has argued that legally, it’s a tax.

“Congress should not be permitted to secure and cast politically difficult votes on controversial legislation by deliberately calling something one thing, after which the defenders of that legislation take an “Alice-in-Wonderland” tack and argue in court that Congress really meant something else entirely, thereby circumventing the safeguard that exists to keep their broad power in check,” he wrote.

Vinson ruled that it’s a penalty, not a tax, and must be defended under the Commerce Clause and not Congress’s taxing authority.

A Dec. 16 trial date is planned in the lawsuit, brought by 20 state attorneys general and governors. Many legal experts expect it to end up before the U.S. Supreme Court.

Just last week, a Michigan judge struck down a similar challenge to the reform law, arguing that Congress was well within its constitutional authority when it crafted the law. There are several lawsuits against the health law that are working their way through the court system, but the attorney general suit is the highest-profile challenge.

Vinson dismissed three of the states’ challenges, including complaints that the law interferes with state sovereignty as to whether employers must offer insurance; that the law coerces states into setting up insurance exchanges; that the individual mandate violates the states' due process rights.

The states argued in September that the law violates the Constitution by requiring an expansion of the Medicaid program that’s funded in part by the states and for penalizing people for not purchasing health insurance.

Florida Attorney General Bill McCollum, a Republican who lost the state’s gubernatorial primary this summer, filed the suit minutes after President Barack Obama signed the health care bill into law in March.